See also:

• PROTOZOA (Gr. 7rpwros, first, and i'woe, living thing)

PROTOZOA (Gr. 7rpwros, first, and i'woe, living thing)  , the name given by See also:

• MODERN

modern zoologists to the animalcules, for the most See also:

• PART

part microscopic, which were termed by the older naturalists See also:

• INFUSORIA

Infusoria, from the manner in which they appear in infusions containing decaying See also:

• ANIMAL
• ANIMAL (Lat. animalis, from anima, breath, soul)

animal and See also:

• VEGETABLE

vegetable See also:

• MATTER

matter . The name Infusoria is now, however, restricted to one of the four classes which comprise the See also:

• PROTOZOA (Gr. 7rpwros, first, and i'woe, living thing)

Protozoa proper . The name Protozoa was coined as far back as 182o as an See also:

• EQUIVALENT

equivalent for the See also:

• GERMAN
• GERMAN, DUTCH AND SCANDINAVIAN

German word Urthiere, meaning animals of See also:

• PRIMITIVE

primitive or archaic nature, the forms of animal See also:

• LIFE

life which may be supposed to have been the first that appeared upon our globe . The See also:

• GREAT

great naturalist C . T. von See also:

• SIEBOLD, CARL THEODOR ERNST VON (1804–1885)
• SIEBOLD, PHILIPP FRANZ VON (1796-1866)

Siebold was, however, the first to give a scientific See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition to the See also:

• GROUP

group . Von Siebold pointed out that in the Protozoa the individual was always a single vital unit or See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell, in contrast with the higher See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

division of the animal See also:

• KINGDOM

kingdom, the Metazoa, in which the See also:

• BODY

body is generally, though not universally, regarded as composed of many such See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units . To put the matter briefly and somewhat technically: the Protozoa are unicellular animals, the Metazoa multicellular animals; in the Protozoa the cell is See also:

• COMPLETE

complete in itself, both morphologically and physiologically, and is capable of maintaining a See also:

• SEPARATE

separate and See also:

• INDEPENDENT

independent existence in suitable surroundings, like any other organism; in the Metazoa the cells are differentiated for the performance of distinct functions and combined together to See also:

• FORM (Lat. forma)

form the various tissues of which the body is built up, and the individual cells of the Metazoan body are not capable of maintaining a separate existence apart from their See also:

• FELLOWS, SIR CHARLES (1799-1860)

fellows . This is the sense in which the See also:

• TERM

term Protozoa is used by zoologists, whereby certain forms of animal life, which were formerly ranked as Protozoa, such as See also:

• SPONGES

sponges and rotifers, are now definitely excluded from the group and classed as Metazoa . The animal kingdom may be divided, therefore, into two sub-kingdoms, the Protozoa and the Metazoa, the first-named characterized by their essentially unicellular nature . This is a criterion by which it is easy to define the Protozoa from a purely zoological standpoint, but which becomes less satisfactory when we take into See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration the whole range of microscopic unicellular organisms . Besides the true Protozoa, which, ex hypothesi, are organisms of animal nature, there are many other organisms of equally See also:

• SIMPLE

simple organization, including the Bacteria and the unicellular See also:

• PLANTS

plants . The Bacteria stand sharply apart from the other forms of life, not only, in many cases, by their divergent methods of See also:

• METABOLISM (from Gr. ,uera(3oXh, change)

metabolism, but by morphological characteristics, such as the definite body-form limited by a distinct envelope, the See also:

• ABSENCE (Lat. absentia)

absence of See also:

• ORGANS

organs for locomotion other than the See also:

• PECULIAR

peculiar flagella, and, above all, by the lack of any differentiation of the body-See also:

• PROTOPLASM

protoplasm into See also:

• NUCLEUS (Lat. for the kernal of a nut, nux, the stone of fruit)

nucleus and cytoplasm, as in all true cells of either animal or vegetable nature .

On the other See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, to separate by hard-and-fast See also:

• DEFINITIONS

definitions the unicellular plants from the unicellular animals is not only difficult but practically impossible . The essential difference between plant and animal is a physiological one, a difference in the method of See also:

• NUTRITION

nutrition . A typical See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green plant is able to live independently of other organisms and to build up its substance from simple gases in the See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air and inorganic salts in the See also:

• SOIL

soil or See also:

• WATER

water, provided that certain conditions of See also:

• LIGHT

light and moisture be See also:

• PRESENT

present in its environment; this is the so-called holophytic method of nutrition . A typical animal, on the other hand, while practically independent of sunlight, is not able to exist apart from other living organisms, since it is not able to build up its substance from simple chemical constituents like a plant, but must be supplied with ready-made proteids in its See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

food, for which it requires other organisms, either plants or animals; this is the so-called holozoic method of nutrition . Intermediate between these two habits of life is the so-called saprophytic See also:

• HABIT (through the French from Lat. habitus, from habere, to have, hold, or, in a reflective sense, to be in a certain condition; in many of the English senses the French use habitude, not habit)

habit, exemplified by the See also:

• FUNGI (p1. of Lat. fungus, a mushroom)

fungi amongst plants; in this method of nutrition the organism cannot build up its substance entirely from inorganic substances, but absorbs the organic substances present in solutions containing organic salts or decaying animal or vegetable matter . If we regard the organisms termed collectively Protozoa from the point of view of their methods of nutrition (considering for the present only See also:

• FREE

free-living, non-parasitic forms), we find in one class, the See also:

• FLAGELLATA

Flagellata, examples of the three methods mentioned above, the holozoic, holophytic and saprophytic habit of life, not only in See also:

• SPECIES

species closely allied to each other, but even combined in one and the same species at different periods of its life or in different surroundings . An individual of a given species may contain See also:

• CHLOROPHYLL (from Gr. XAwpos, green, 4bXXov, a leaf)

chlorophyll, with which it decomposes carbonic See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid See also:

• GAS

gas in the sunlight, like a plant, while possessing a definite mouth-See also:

• APERTURE (from Lat. aperire, to open)

aperture, by means of which it can ingest solid food, like an animal . Such instances show clearly that in the simplest forms of life the difference between plant and animal is but a difference of habit and of mode of nutrition, to which the organism is not at first irrevocably committed, and which are not at first accompanied by distinctive morphological characteristics . Only when the organism becomes specialized for one or the other mode of life exclusively does it acquire such definite morphological characters that the difference between plant and animal can be used for the purpose of a natural See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification, as in the higher forms of life . In the lowest forms it is not possible to See also:

• BASE

base natural subdivisions on their vegetable or animal nature . - For this See also:

• REASON (Lat. ratio, through French raison)

reason it has been proposed by E . See also:

• HAECKEL, ERNST HEINRICH (1834- )

Haeckel to unite all the primitive forms of life in which the body is morphologically equivalent to a single cell into one group, the See also:

• PROTISTA

Protista, irrespective of their animal or vegetable nature .

In this method of dealing with the problem the Protista are regarded as a distinct kingdom (Reich), more or less inter-mediate between, but distinct from, the animal and vegetable kingdoms, and representing the ancestral stock from which both animals and plants have sprung . Many authorities have followed Haeckel's See also:

• LEAD
• LEAD (pronounced iced)

lead in the matter, and the See also:

• SCIENCE (Lat. scientia, from scire; to learn, know)

science of Protistology or Protistenkunde has already a See also:

• SPECIAL

special See also:

• JOURNAL
• JOURNAL (through Fr. from late Lat. diurnalis, daily)

journal devoted to the publication of researches upon it . But though it may be more scientific, from a theoretical point of view, to group all these primitive organisms together in the way suggested by Haeckel, in practice it is inconvenient, on See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account of thevast number of forms of life to be comprised as Protista, their diversity in habit of life and organization, and, above all, the difference in the technical methods required for their study, which becomes too complicated for a single worker . Hence Protistology becomes split up in practice by its own See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass into three sciences: the Bacteria are the See also:

• OBJECTS

objects of the science of See also:

• BACTERIOLOGY

bacteriology; botanists See also:

• DEAL

deal with the unicellular plants; and the zoologists with those Protista which are more distinctly animal in their characters . Hence the Protozoa are to be regarded as a convenient rather than a natural group, and may be characterized generally as follows: Organisms in which the individual is a single cell, that is to say, consists of a single undivided mass of protoplasm which is capable of independent existence in a suitable environment; if many such individuals be combined together to form a See also:

• COLONY (Lat. colonia, from colonus, a cultivator)

colony, as frequently occurs, there is no differentiation of the individuals except for reproductive purposes, and never for See also:

• TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue-formation as in the Metazoa . The body always contains chromatin or nuclear substance, which may be disposed in various ways, but usually forms one or more concentrated masses termed nuclei, which can be distinguished sharply from the See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general body-protoplasm or cytoplasm . The protoplasmic body may be naked at the See also:

• SURFACE

surface, or maybe limited and enclosed by a distinct envelope or cell-membrane, which is not usually of the nature of See also:

• CELLULOSE

cellulose, except in holophytic forms . Organs serving for locomotion and for the See also:

• CAPTURE (from Lat. capere, to take; Fr. prise maritime; Ger. Wegnahme)

capture and assimilation of solid food are usually present, but may be wanting altogether when the mode of nutrition is other than holozoic; chlorophyll, on the other hand, is only found as a constituent of the body-substance in the holophytic Flagellata.' To these characters it may be added that See also:

• REPRODUCTION

reproduction is effected by some form of fission, or division of the body into smaller portions, and that in the vast See also:

• MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of Protozoa, if not in all, a See also:

• PROCESS

process of conjugation or syngamy occurs at some See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period in the life-See also:

• CYCLE
• CYCLE (Gr. KUK)^os, a circle)

cycle, the essential feature of the process being See also:

• FUSION

fusion of nuclear matter from distinct individuals . The foregoing definition does not distinguish the Protozoa sharply from the primitive forms of plant-life, with which, as stated above, they are connected by many transitions; but the differentiation of the body-substance into nucleus and cytoplasm separates them at once from the Bacteria, in which the chromatin is distributed evenly through the body-protoplasm . Protozoa and Disease.—The study of the Protozoa has acquired great See also:

• PRACTICAL

practical importance from the fact that many of them live as parasites of other animals, and as such may be the cause of dangerous diseases and epidemics in the higher forms of animal life and in See also:

• MAN
• MAN, ISLE OF (anc. Mona)

man (see PARASITIC DISEASES) . Examples of parasitic forms are to be found in all the four classes into which, as will be stated below, the Protozoa are divided, and one class, the See also:

• SPOROZOA

Sporozoa, is composed entirely of endoparasitic forms . Hence Protozoology, as it is termed, is rapidly assuming an importance in medical and veterinary science almost equal to that of bacteriology, although the recognition of Protozoa as agents in the See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of disease is hardly older than a See also:

• DECADE (from Gr. Oka, ten)

decade .

The most striking instances of Protozoa well established as pathogenic agents are the malarial parasites, the species of Piro plasma causing haemoglobinuria of See also:

• CATTLE (Norman Fr. catel, from Late Lat. capitale, wealth or property, a word applied in the feudal system to movable property and particularly to live stock, and surviving in its wider meaning as " chattel " or " chattle ")

cattle and other animals, the See also:

• TRYPANOSOMES, or HAEMOFLAGELLATES

trypanosomes causing tsetse-See also:

• FLY (formed on the root of the supposed original Tent. fleugan, to fly)

fly disease, surra, sleeping' sickness, and other maladies, the species of Leishmania causing kala azar and See also:

• ORIENTAL

oriental sore, and the See also:

• AMOEBA

Amoeba responsible for the so-called amoebic See also:

• DYSENTERY (from the Gr. prefix Ova-, in the sense of " bad," and Evmpov, the intestine)

dysentery . Other diseases referred, but as yet doubtfully, to the agency of Protozoa are syphilis, small-pox, See also:

• HYDROPHOBIA (Gr. iibwp, water, and 4osos, fear; so called from the symptom of dread of water), or RABIES (Lat. for" madness ")

hydrophobia, yellow See also:

• FEVER (Lat. febris, connected with fervere, to burn)

fever, and even See also:

• CANCER (" THE CRAB ")
• CANCER, LUIS (d. 1549)
• CANCER, or CARCINOMA (from Lat. cancer, Gr. KapKivwga, an eating ulcer)

cancer . It is only possible here to discuss briefly in a general way the relations of these parasites to their hosts . When two organisms stand habitually in the relation of See also:

• HOST

host and See also:

• PARASITE (From Gr. irapa, beside, Tiros food)

parasite, an See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium tends to become established gradually between them, so 1 Many Protozoa contain symbiotic green organisms, so-called zoochlorellae or zooxanthellae, in their body-protoplasm; for instance, See also:

• RADIOLARIA

Radiolaria, and See also:

• CILIATA
• CILIATA (M. Pertz)

Ciliata such as See also:

• PARAMECIUM, O

Paramecium bursaria, &e . This See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition must be carefully distinguished from chlorophyll occurring as a cell-constituent . that a condition is brought about in which, after many generations, the host becomes " tolerant " of the parasite, and the parasite is not lethal to the host, though perhaps capable of setting up considerable disturbance in its vital functions . Many animals are found to contain almost constantly certain See also:

• INTERNAL

internal parasites without being, apparently, in the least affected by them; and it should be See also:

• BORNE, KARL LUDWIG (1786–1837)

borne in mind that in most cases it is not to the See also:

• INTEREST

interest of the parasite to destroy the host or to over-tax its resources . But when the parasite is transferred naturally or artificially to a species or See also:

• RACE

race of host which does not ordinarily See also:

• HARBOUR (from M.E. hereberge, here, an army; cf. Ger. Heer and -beorg, protection or shelter. Other early forms in English were herberwe and haiborow, as seen in various place names, such as Market Harborough.. The French auberge, an inn, derived through

harbour it, and which therefore has not acquired See also:

• POWERS, HIRAM (1805-1873)

powers of resisting its attacks, the parasites may be most deadly in their effects . Thus the See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white traveller in the tropics is exposed to far greater dangers from the indigenous disease-producing organisms than are the natives of those climes . In some cases two organisms have become mutually adapted to each other as host and parasite to such an extent that the parasite is not capable of flourishing in any other host . An instance of this is Trypanosoma lewisi of the See also:

• RAT (a word common to Teut. and Rom. languages; probably first adopted in Teut.; the ultimate origin is not known; Skeat suggests the root rad-, to scratch; cf. Ger. Ratte, Dan. rotte, Fr. rat, &c.)

rat, which cannot live in an'y other species of animal but a rat, and which is not as a See also:

• RULE

rule lethal to a rat, at least not to one otherwise healthy . Contrasting in an instructive manner with this species is Trypanosoma brucii, which occurs as a natural parasite of buffaloes and other big See also:

• GAME

game in See also:

• AFRICA
• AFRICA, ROMAN

Africa, and is, apparently, harmless to them, but which is capable of being transferred to other animals by inoculation .

The transference may take See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place naturally, by the bite of a tsetse-fly, or may be effected artificially; in either See also:

• CASE
• CASE, JOHN (d. 1600)

case T. brucii is extremely lethal to certain animals, such as imported cattle, horses and See also:

• DOGS, ISLE OF

dogs, or to rats and See also:

• GUINEA

guinea-pigs . Other animals, however, may be quite " repellent "I to this parasite, that is to say, if it be inoculated into their See also:

• BLOOD

blood it See also:

• DIES, CHRISTOPH ALBERT (1755-1822)

dies out without producing See also:

• ILL

ill effects, just as T. lewisi does when injected into an animal other than a rat . Thus it is seen that T. brucii, when introduced into the blood of an animal which is specifically or racially distinct from its natural hosts in the region where it is indigenous, is either unable to maintain itself in its new host, or flourishes in it to such an extent as to be the cause of its See also:

• DEATH

death . We may assume, therefore, at least as a working See also:

• HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

hypothesis, that a lethal parasite is one that is new to its host, and that a harmless parasite is one See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long established . Since all parasites must have been new to their proper hosts at some period, See also:

• RECENT

recent or remote, in the See also:

• HISTORY

history of the species, it would follow that the first commencement of See also:

• PARASITISM

parasitism would be in almost all cases a life and death struggle, as it were, between the two organisms concerned, and it is quite conceivable that the host might succumb in the struggle and so be exterminated . See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

Ray Lankester has suggested that the extinction of many species of animals in the past may have been due, in some cases, to their having been attacked by a species of parasite to which they did not succeed in becoming adapted, and by which they became, in consequence, exterminated entirely . Organization of the Protozoa.—The body-form may be See also:

• CONSTANT, BENJAMIN (1845-1902)

constant or inconstant in the Protozoa, according as the body-substance is or is not limited at the surface by a See also:

• FIRM

firm envelope or cuticle . When the surface of the protoplasm is naked, as in the See also:

• COMMON

common amoeba and allied organisms, the movements of the animal bring about continual changes of form . The protoplasm flows out at any point into processes termed pseudopodia, which are being continually retracted and formed anew . Such movements are known as amoeboid, and may be seen in the cells of Metazoa as well as in Protozoa . The pseudopodia serve both for locomotion and for the capture of food . If equally See also:

• DEVELOPED

developed on all sides of the body, the animal as a whole remains stationary, but if formed more on one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side than the other, the mass of the body shifts its position in that direction, but the See also:

• MOVEMENT

movement of See also:

• TRANSLATION

translation is generally slow .

If the animal remains perfectly quiescent and inactive, the See also:

• LAWS

laws of surface-tension acting upon the semi-fluid protoplasmic body cause it to assume a simple spherical I The use of the terms " tolerant " and " repellent " is taken from the excellent See also:

• ARTICLE (from Lat. articulus, a joint)

article on " Sleeping Sickness," by E . Ray Lankester, in the Quarterly See also:

• REVIEW (Fr. revue, from revoir, to see again, Lat. re and videre)

Review (See also:

• JULY

July 1904), No . 399. pp . 113-138 . In the majority of Protozoa, however, the protoplasm is limited at the surface by a firm membrane or cuticle, and in consequence the body has a definite form, which varies greatly in different species, according to the habit of life . As a general rule those forms that are fixed and sedentary in habit tend towards a radially symmetrical structure; those that are free-See also:

• SWIMMING (from " swim," A.S. swimman, the root being common in Teutonic languages)

swimming approach to an ovoid form, with the longest See also:

• AXIS (Lat. for " axle ")

axis of the body placed in the direction of movement; and those that creep upon a firm substratum have the See also:

• LOWER

lower side of the body flattened, so that dorsal and ventral surfaces can be distinguished; it is very rare, however, to find a bilaterally symmetrical type of body-structure amongst these organisms . In some cases the cuticle may be too thin to check completely the changes of form due to the movements of the underlying protoplasm; instances of this are seen amongst the so-called " metabolic " Flagellata, in which the body exhibits continually changes of form, termed by Lankester " euglenoid " movements, due to the activity of the superficial contractile layer of the body manifesting itself in See also:

• RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring-like contractions passing down the body in a manner similar to the peristaltic movements of the See also:

• INTESTINE (Lat. intestinus, internal, usually in neuter plural intestina. from intus, within)

intestine . The body-substance of the Protozoa is protoplasm, or, as it was originally termed by Dujardin, sarcode, which is finely alveolar in structure, the See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter of the alveoli varying generally between z and r µ . At the surface of the body the alveoli may take on a definite See also:

• HONEYCOMB

honeycomb-like arrangement, forming a special " alveolar layer " which in See also:

• OPTICAL

optical See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section appears radially striated . Besides the See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute protoplasmic alveoli, the protoplasm often shows a coarse vacuolation throughout the whole or a part of its substance, giving the body a frothy structure . When such vacuoles are present they must be carefully distinguished from the contractile vacuoles and food-vacuoles described below; from the former they differ by their non-contractile nature, and from the latter by not containing food-substances . In many Protozoa and especially in those forms in which there is no cuticle, the body may be supported by a See also:

• SKELETON

skeleton .

The material of the skeleton differs greatly in different cases, and may be wholly of an organic nature, or may be impregnated with, or almost entirely composed of, inorganic See also:

• MINERAL

mineral salts, in which case the skeletal substance is usually either See also:

• SILICA

silica or carbonate of See also:

• LIME
• LIME (O. Eng. lim, Lat. limes, mud, from linere, to smear)

lime . From the morphological point of view the skeletons of Protozoa may be divided into two See also:

• PRINCIPAL

principal classes, according as they are formed internal to, or See also:

• EXTERNAL

external to, the body in each case . Instances of internal skeletons are best seen in the spherical floating forms comprised in the orders Radiolaria and See also:

• HELIOZOA

Heliozoa; such skeletons usually take the form of spicules, radiating from the centre to the circumference, and often further strengthened by the for. mation of tangential bars, producing by their See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union a lattice-See also:

• WORK

work, which in species of relatively large See also:

• SIZE

size may be formed periodically at the surface as the animal grows so that the entire skeleton takes the form of concentric hollow See also:

• SPHERES, MUSIC OF THE

spheres held together by radiating beams . The architectural types of these skeletons show, however, an almost See also:

• INFINITE (from Lat. in, not, finis, end or limit; cf. findere, to deave)

infinite diversity, and cannot be summarized briefly . External skeletons have usually the form of a See also:

• SHELL
• SHELL (O. Eng. scell, scyll, cf. Du. sceel, shell, Goth. skalja, tile; the word means originally a thin flake,. cf. Swed. skalja, to peel off; it is allied to " scale " and " skill," from a root meaning to cleave, divide, separate)

shell or See also:

• HOUSE
• HOUSE (O. Eng. hiss, a word common to Teutonic languages, cf. Dut. huis, Ger. Haus; in Gothic it is only found in gudhiss, a temple; it may be ultimately connected with the root of " hide," conceal)

house, into which the body can be retracted for See also:

• PROTECTION

protection, and from which the protoplasm can issue forth during the animal's phases of activity . Shells of this See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind, which must be carefully distinguished from cuticles or other membranes that invest the body closely, are well seen in the See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order See also:

• FORAMINIFERA

Foraminifera; in the simplest cases they are monaxon in See also:

• ARCHITECTURE (Lat. architectura, from the Gr. ap)(LTEKrwv, a master-builder)

architecture, that is to say, with one principal axis See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round which the shell is radially symmetrical, and at one See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

pole is a large aperture through which the protoplasm can creep out . In addition to the principal aperture, the shell may or may not be pierced all over by numerous See also:

• FINE

fine pores, through which also the protoplasm can pass out . For further details concerning these shells and their very numerous varieties of structure the reader is referred to the article FORAMINIFERA . The protoplasmic body of the Protozoa is frequently differ- of the nuclear apparatus set apart as a distinct kinetic nucleus, entiated into two zones or regions: a more external, termed the with the See also:

• FUNCTION

function, apparently, of governing the activities of ectoplasm or ectosarc, and a more internal, termed the endo- the flagellum . plasm or endosarc . The ectosarc is distinguished by being See also:

• CILIA (plural of Lat. cilium, eyelash)

Cilia are minute, See also:

• HAIR (a word common to Teutonic languages)

hair-like extensions of the ectoplasm, which more clear and hyaline in See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance, and more tough and viscid See also:

• PIERCE, FRANKLIN (1804—1869)

pierce the cuticle and form typically a furry covering to the body. in consistence; the endoplasm, on the other hand, is more I Though perhaps primitively derived from flagella, cilia, in their granular and opaque, and of a more fluid nature . The ecto- usual form, are distinguished from flagella by being of smaller plasm is the protective layer of the body, and is also the portion size, by being present, as a rule, in much greater See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers, and most concerned in movement, in See also:

• EXCRETION (Lat. ex, out of, cernere, cretum, to separate)

excretion, and perhaps also above all by the See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character of their movements .

In the place in sensation and in functions similar to those performed by the of the complicated lashing movements of the flagella, each cilium See also:

• NERVOUS

nervous systems of higher animals . The endoplasm, on the performs a simple stroke in one direction, becoming first bowed other hand, is the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief seat of See also:

• DIGESTIVE

digestive and reproductive on one side, by an See also:

• ACT (Lat. actus, actum)

act of contraction, and then straightened functions. out again when relaxed . The movements of the cilia are co- As the protective layer of the body, the ectoplasm forms ordinated and they act in See also:

• CONCERT (through the French from Lat. con-, with, and certare, to strive)

concert, though not absolutely in the envelopes or membranes which invest the surface of the body, unison, each one contracting just before or after its See also:

• NEIGHBOUR (O. Eng. neahgebiir, from Walt, " nigh," " near ")

neighbour, and which are differentiations of the outermost layer of the so that waves of movement pass over a ciliated surface in a ectoplasm . Thus in most Flagellata the ectoplasm is represented given direction, similar to what may be seen in a cornfield when only by the more or less firm See also:

• OUTER

outer covering or periplast . Even the See also:

• WIND
• WIND (a common Teut. word, cognate with Skt. vats, Lat. ventus, cf. " weather," to be of course distinguished from to " wind," to coil or twist, O.Eng. windan, cf. "wander," "wend," &c.)

wind is blowing over it . Primitively coating the whole when such envelopes are absent, however, the ectoplasm can surface of the body evenly, the'cilia may become modified and still be seen to exert a protective function; as, for instance, in specialized in various ways, which cannot be described in detail those Myxosporidia which are parasitic in the See also:

• GALL (a word common to many Teutonic languages, cf. Dutch gal, and Ger. Galle; the Indo-European root appears in Gr. xoXi,, and Lat. fel; possibly connected with " yellow," with reference to the colour of bile)
• GALL, FRANZ JOSEPH (1758-1828)

gall-bladders or here (see INFUSORIA) . urinary bladders of their hosts, and which can resist the See also:

• ACTION

action Besides the organs of locomotion already mentioned, there of the juices in which they live so long as the ectoplasm is intact, may be present so-called undulating membranes, in the form but succumb to the action of the See also:

• MEDIUM

medium if the ectoplasm be of thin sheets of ectoplasm which are capable of performing injured . In many Infusoria the ectoplasm contains special sinuous, undulating movements by their inherent contractility. organs of offence termed trichocysts, each a minute ovoid body In some cases distinct contractile threads or See also:

• MYONEMES

myonemes have from which, on stimulation, a See also:

• THREAD (0. Eng. praed, literally, that which is twisted, prawan, to twist, to throw, cf. " throwster," a silk-winder, Ger. drehen, to twist, turn, Du. draad, Ger. Draht, thread, wire)

thread is shot out, in a manner been described in these membranes . Undulating membranes similar to the nematocysts of Coelenterata . Similar organs I appear to be formed either by the fusion together of a See also:

• ROW, JOHN (c. 1525—1580)

row of are seen also in the spores of Myxosporidia, as the so-called polar cilia, side by side,. or by the See also:

• ATTACHMENT

attachment of a flagellum to the capsules; but in this case the organs are not specially ectoplasmic, body by means of an ectoplasmic See also:

• WEB (a word common to Teutonic languages, cf. Du. webbe, Dan. vaev, Ger. Gewebe, all from the Teutonic wabh—to weave)

web, in which case the flageland appear to serve for See also:

• ADHESION (from Lat. adhaerere, to adhere)

adhesion and attachment, rather than lum forms the free edge of the membrane, as in the genus for offence . Trypanosoma . The connexion of the ectoplasm with movement is seen in the Returning to the ectoplasm, the excretory function exerted simplest forms, such as Amoeba, by the fact that all pseudopodia by this layer is seen by the formation in it of the peculiar See also:

• CON

con-arise from it in the first instance .

In forms with a definite tractile vacuoles found in most free-living Protozoa . A con- cuticle, on the other hand, the ectoplasm usually contains contractile See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres or myonemes, forming, as it were, the See also:

• MUSCULAR

muscular See also:

• SYSTEM

system of the organism . The dependence of the motility of the animal upon the development of the ectoplasm is well seen in See also:

• GREGARINES (mod. Lat. Gregarina, from gregarius, collecting in a flock or herd, grex)

Gregarines, in which other organs of locomotion are absent; in forms endowed with active powers of locomotion a distinct limit of its growth it discharges its contents to the exterior by ectoplasmic layer is present below the cuticle; in those Gregarines a sudden and rapid contraction . There is, apparently, in most incapable of active movement, on the other hand, the ectoplasm if not in all cases, a definite See also:

• PORE

pore through which the contractile vacuole empties itself to the exterior . On account of the relatively large size which the contractile vacuole attains it bulges inwards beyond the limits of the ectoplasm and comes to See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

lie chiefly in the endoplasm, to which it is sometimes, but erroneously, ascribed . In the most highly differentiated Protozoa, for instance, the Ciliata, the ectoplasm contains an apparatus of excretory channels, situated in its deeper layers, and forming as it were a drainage-system, from which the contractile vacuoles are fed . The fluid discharged by the contractile vacuoles appears to be chiefly water which has been absorbed at the surface of the protoplasmic body, and which has filtered through the protoplasm, taking up the soluble See also:

• WASTE (O. Fr. wast, guast, gast, gaste; Lat. vastus, vast, desolate)

waste nitrogenous products of the metabolism and the gaseous products of respiration; hence the contractile vacuoles may be compared in a general way to the urinary and See also:

• RESPIRATORY

respiratory organs of the Metazoa . One of the first consequences of the parasitic habit of life is the disappearance of the contractile vacuoles, which are hardly ever found in truly parasitic Protozoa, that is to say, in forms which live in the interior of other animals and nourish them-selves at their expense . They are also very frequently absent in marine forms . Mechanisms of a nervous nature are very seldom found in Protozoa, but in some Ciliata special tactile bristles are found, and it is possible that flagella, and perhaps even pseudopodia, may be sometimes tactile rather than locomotor in function . Pigment-spots, apparently sensitive to light, may also occur in some Flagellata . The endoplasm, as already stated, is the chief seat of nutritive and reproductive processes .

In many Flagellata the ectoplasm tractile vacuole is a spherical drop of watery fluid which makes its appearance periodically at some particular spot near the surface of the animal's body, or, if more than one such vacuole is present, at several definite and constant places . Each vacuole grows to a certain size, and when it has reached the is absent or scarcely recognizable . From the ectoplasm arise the special organs of locomotion, which, when present, take the form of pseudopodia, flagella or cilia . Pseudopodia, as already explained, are temporary protoplasmic organs which can be extruded or retracted at any point; they fall naturally into two principal types, between which, however, transitions are to be found: first, slender, filamentous or filose pseudopodia, composed of ectoplasm alone, which may remain separate from one another, or may anastomose to form networks, and are then termed reticulose; secondly, thick, See also:

• BLUNT, JOHN HENRY (1823–1884)
• BLUNT, JOHN JAMES (1794–1855)
• BLUNT, WILFRID SCAWEN (184o— )

blunt, so-called lobose pseudopodia, which are composed of ectoplasm with a core of endoplasm, and never form networks . In forms showing active locomotor powers the pseudopodia are usually more lobose in type; filose pseudopodia, on the other hand, are more adapted for the function of capturing food . Flagella are long, slender, vibratile filaments, generally few in number when present, and usually placed at the pole of the body which is anterior in progression . Each flagellum performs peculiar lashing movements which cause the body, if free, to be dragged along after the flagellum in jerks or leaps; if, however, the body be fixed, the action of the flagellum or flagella causes a current towards it, by which means the animal obtains its food-See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply . A flagellum which is anterior in movement has been distinguished by Lankester by the convenient term tractellum; sometimes, however, the flagellum is posterior in movement and acts as a propeller, like the tail of a See also:

• FISH (O. Eng. fist, a word common to Teutonic languages, cf. Dutch visch, Ger. Fisch, Goth. fisks, cognate with the Lat. piscis)
• FISH, HAMILTON (1808-1893)

fish; for this type Lankester has proposed the term pulsellum . The flagellum appears to arise in all cases from a distinct basal granule, and in some cases, as in the genus Trypanosoma, there is a portion is represented only by the thin envelope or periplast, so that the whole body is practically endoplasm . When the two layers are well differentiated the endoplasm is more fluid and coarsely granular, and contains various organs, chief amongst them in importance being the nucleus, which must be considered specially and may be put aside for the present . In considering the functions of ingestion and assimilation of food a distinction must be See also:

• DRAWN

drawn between those Protozoa which absorb solid food-particles, that is to say, which are holozoic in habit, and those which, being holophytic, saprophytic or parasitic in habit, absorb their nourishment in a See also:

• STATE
• STATE, GREAT OFFICERS OF

state of See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution . Only in holozoic forms is a special apparatus found for ingestion or digestion of food; in all other forms nutriment is absorbed by osmosis through the body-See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall, presumably at any point of the surface .

In holozoic forms we must distinguish further those in which the protoplasm is naked at the surface from those in which the body is clothed by a firm cuticle or cell-membrane . In naked forms food-particles are taken in at any point of the body-surface, either by means of the pseudopodia, or by the action of flagella causing them to impinge upon the surface of the body . In either case the food is absorbed by the protoplasm simply flowing round it and engulfing it, and the food passes into the interior of the body in a tiny droplet of water forming what is termed a food-vacuole . Into the food-vacuole the surrounding protoplasm secretes digestive enzymes, so that each such vacuole represents a minute digestive cavity, in which the food is slowly digested, rendered soluble, and absorbed by the surrounding protoplasm . The insoluble See also:

• RESIDUE (through the French, from the Lat. residuum, a remainder, from residere, to remain)

residue of the food is finally rejected by expelling the food-vacuole and its contents from the surface of the body at any convenient point . The simple process of food-absorption described above for the more primitive naked forms is necessarily modified in detail, though not in principle, in corticate Protozoa, that is to say, in forms provided with a cuticle . In the first place, it becomes necessary to have a special aperture for the ingestion of food, a cell-mouth or cytostome . Primitively the cytostome is a simple pore or interruption of the cuticle, but in forms more highly evolved the aperture is prolonged inwards in the form of a See also:

• TUBE (Lat. tuba)

tube lined by ectosarc and cuticle, forming a gullet or See also:

• OESOPHAGUS (Gr. o'lvca=I will carry, and r/)ayeiv, to eat)

oesophagus which ends in the endoplasm . Food-particles are forced by the action of cilia or flagella down the oesophagus and collect at the bottom of it in a droplet of water which, after reaching a certain size, passes into the endoplasm as a food-vacuole in which the food is digested . For rejection of the insoluble residue of the food-vacuoles, a special pore or cell-anus (cvtopyge) may be present . In the Ciliata there is often a distinct anal tube visible at all times, but as a rule the anus is only visible at the moment that faecal matter is being ejected from it, though fine sections show that the pore is a constant one . In the higher Flagellata, on the other hand, the oesophageal ingrowth forms commonly a sort of cloacal cavity, into which the contractile vacuole or vacuoles See also:

• DISCHARGE (adapted from the O. Fr. discharge, modern decharge, from a med. Lat. discargare, to unload, dis- and earn care, to load, cf. " charge ")

discharge themselves, and into which also the food-vacuoles evacuate their residues .

Besides the food-vacuoles already described, and the nuclear apparatus presently to be dealt with, the endoplasm may contain various metaplastic products, that is to say, bodies to be regarded as stages in the upward or downward metabolism of the proto-. plasmic substance . Such substances may take the form of coarse granules of various kinds, crystals, vacuoles or droplets of fatty or oily nature, pigment-grains, and other bodies . In the holophytic Flagellata the endoplasm contains also various organs proper to the vegetable cell, such as chlorophyll-bodies (chromatophores), pyrenoids, grains of a starchy nature (paramylum), and so forth, which need not be described here in detail . The nucleus in Protozoa is usually a compact, fairly conspicuous structure, composed of chromatin combined in various ways with an achromatic substance or substances . Sometimes the chromatin is distributed in smaller masses through the nucleus, producing a granular type of nucleus; more often the chromatin is more or less concentrated in a central mass forming a so-calledkaryosome, consisting of an achromatic plastinoid substance impregnated with chromatin . If the karyosome is large and there is very little chromatin between it and the nuclear membrane, the nucleus is of the type termed vesicular . A nuclear membrane is not, however, always present, and true nucleoli, of the type found in the nuclei of metazoan cells, are not found in Protozoa . A given individual may have more than one nucleus, and the number present may amount to many thousands, as in the plasmodia of See also:

• MYCETOZOA (Myxomycetes, Schleimpilze)

Mycetozoa . In such cases the nuclei may be all of one kind, that is to say, not markedly different in size, structure or function, so far as can be seen; or there may be a pronounced morphological differentiation of the nuclei correlated with a difference of function . Thus in the class Infusoria two nuclei are found in each individual; a macronucleus which is somatic in function, that is to say, which regulates the metabolism and vital processes of the body generally, and the micro-nucleus, which is generative in function, that is to say, which remains in reserve during the See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary, " vegetative " life of the organism and becomes active during the act of syngamy, after which the effete macronucleus is absorbed or See also:

• CAST (from the verb meaning " to throw "; the word is Scand. in origin, cf. Dan. kaste, and Swed. kasta; " cast " in Middle Eng. took the place of the A.S. weor pan, cf. Ger. werf en)

cast out and a new somatic nucleus is formed from portions of the micronuclei which have undergone fusion in the sexual act . Thus the micro-nucleus of the Infusoria can be compared in a general way with the germ-plasm of the Metazoa, like which it remains inactive until the sexual union . On the other hand, in some Flagellata a differentiation of the nucleus of quite a different type is seen, a smaller, kinetic nucleus being separated off from the larger, trophic or principal nucleus .

The kinetic nucleus has the function, apparently, of controlling the locomotor apparatus, so that the specialization of these two nuclei is of a kind quite different from that seen in the Infusoria . Besides the nuclear substance which is concentrated to form the principal nucleus or nuclei, there may be present also extranuclear granules of chromatin, so-called chromidia, scatteredt throughout the whole or some part of the protoplasmic body . Chromidia may be normally present in addition to the principal nucleus, or may be formed from the principal nucleus during certain phases of the life-cycle . In some cases the entire nucleus may become resolved temporarily into chromidia, from which a new nucleus may be formed again later by condensation and concentration of the scattered granules . When the chromidia are numerous and closely packed they may form a so-called chromidial network (Chromidial-Netz) . Recent observations on the reproduction of some See also:

• SARCODINA

Sarcodina have shown that the chromidia may possess great importance in the life-cycle as representing generative chromatin which, like the See also:

• MICRONUCLEUS

micronucleus of the Infusoria mentioned above, remains in reserve until, by the process of syngamy, the nuclear apparatus is renewed;; while the principal nuclei represent, like the macronuclei,,, somatic or vegetative chromatin which becomes effete and is cast off or absorbed when syngamy takes place . These questions will be discussed further below . It was formerly supposed that the lowest Protozoa were entirely without a nucleus, and on this supposition E . Haeckel attempted to establish a class named by him Monera, defined as Protozoa consisting of protoplasm alone, in which a nucleus was not differentiated . To this class were referred various organisms whose alleged archaic nature was expressed by such names as See also:

• PROTOGENES
• PROTOGENES (E. Haeckel)

Protogenes primordialis, organisms which, like so many other of the primitive forms of animal life described by Haeckel, have been seen by that naturalist alone up to the present . In all Protozoa that have been examined by modern methods a nucleus in some form has been demonstrated to exist, and it must be supposed, until See also:

• PROOF (in M. Eng. preove, proeve, preve, &°c., from O. Fr . prueve, proeve, &c., mod. preuve, Late. Lat. proba, probate, to prove, to test the goodness of anything, probus, good)

proof to the contrary be forthcoming, that in the case of the so-called Monera either the nucleus was overlooked owing to defective technique, or it had been temporarily resolved into chromidia . The nuclear apparatus may be supplemented by other bodies of which the nature is not always clear .

Such is the so-called " Nebenkern " of Paramoeba eilhardi, apparently of the nature of a centrosome . Sometimes the karyosome acts like a . centrosome during the division of the nucleus, and sometimes in a general way, but can be given special names in special cases true centrosomes are present . Flagella also commonly arise from basal granules of a centrosomic nature, blepharoplasts in the correct sense of the term;l these blepharoplasts are always in connexion with the nucleus, or with the kinetic nucleus if there is one distinct from the trophic nucleus, as in the genus Trypanosoma and allied forms . Reproduction of the Protozoa.—The mode of reproduction in these organisms is the same as that of the cell generally, and takes always the form of fission of some kind; that is to say, of division of the body into smaller portions, each of which represents a See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

young individual . The division of the body is preceded by that of the nucleus, if single, or of each nucleus in; the cases where there are two different nuclei; if, however, more than one nucleus of the same kind be present, the nuclei may be simply shared amongst the daughter-individuals, this mode of division being known as plasmotomy . Other organs of the body may either, like the nucleus, undergo fission, or may be formed afresh in the daughter-individuals . The division of the nucleus in Protozoa may take place by the See also:

• DIRECT

direct method or by means of mitosis . Direct division, without mitosis, is of very common occurrence; the division may be simple or multiple, that is to say, into only two parts, or into a number of fragments formed simultaneously . An extreme case of multiple fission is seen in the formation of the microgametes of Coccidium schubergi, where the nucleus breaks up into a great number of chromidia, which become concentrated in patches to form the several daughter-nuclei . In some cases, on the other hand, multiple daughter-nuclei are formed by rapidly repeated simple division of the See also:

• PARENT, SIMON NAPOLEON (1855– )

parent nucleus . The mode of division may be different in different nuclei of the same individual; thus in the Infusoria the macronucleus divides by direct division, the micronucleus by mitosis .

The mitosis of the Protozoa is far from being of the See also:

• UNIFORM

uniform stereotyped See also:

• PATTERN

pattern seen in the Metazoa, but, as might have been expected, often shows a much simpler and more primitive condition . Centrosomes are often absent, and their place may be taken, as stated above, by other bodies . The nuclear membrane may be retained throughout the mitosis . Definite chromosomes can, as a rule, be made out, but the chromosomes are often very numerous and minute, without definite form, and See also:

• DIVIDE

divide irregularly . Much remains to be done in studying the mitosis of the Protozoa, but it is probable that wider knowledge will show many conditions intermediate between direct division and perfect mitosis . The simplest method of fission in Protozoa is that termed binary, where the body divides into two halves, which may be equal and similar, so that the result is two See also:

• SISTER

sister-individuals impossible to distinguish as parent and offspring . In many cases of binary fission, however, the resulting daughter-individuals may be markedly unequal in size, so that one maybe distinguished as the parent, the other as the offspring . If the daughter-individual be relatively very small, and formed in a more or less imperfect condition at first, the process is termed gemmation or budding . The buds formed in this way may be either external, formed on the surface of the body, or internal, that is, formed in special internal cavities, from which the offspring are later set free, as in many Acinetaria . Gemmation may be correlated with multiple nuclear fission in such a way that buds are formed over the whole body surface of the organism, which thereby under-goes a process of simultaneous multiple fission into numerous daughter-individuals . Rapid multiple fission of this kind is termed sporulation, and is a form of reproduction which is of common occurrence, especially in parasitic forms . Usually, the central portion of the parent body remains over as a residual body (Restkorper), but sometimes the parent organism is entirely resolved into the daughter-individuals, which are termed spores ' The kinetic nucleus of Trypanosoma is sometimes, but in the writer's See also:

• OPINION (Lat. opinio, from opinari, to think)

opinion wrongly, named centrosome or blepharoplast; the bodies to which cytologists give these names are achromatic bodies; the kinetic nucleus is a true See also:

• CHROMATIC (Gr. xpcoµaruc6s, coloured, from xpwµa, colour)

chromatic nucleus .

The question of the centrosome in Protozoa is discussed by R . See also:

• GOLDSCHMIDT, HERMANN (1802-1866)

Goldschmidt and M . Popoff . (see GREGARINES, See also:

• COCCIDIA

COCCIDIA, &C.) . Life-cycles of the Protozoa.—It is probable that in all Protozoa, as in the Metazoa, the life-history takes its course in a See also:

• SERIES (a Latin word from serere, to join)

series of recurrent cycles of greater or less extent, a fixed_point, as it were, in the cycle being marked by the act of syngamy, or conjugation, which represents, apparently, a process for recuperation of the waning vital powers of the organism . It is true that in many types of Protozoa syngamy is not known as yet to occur, but in all species which have been thoroughly investigated syngamy in some form has been observed, and there is nothing to lead to the belief that the sexual process is not of universal occurrence in the Protozoa . The life-cycle of a given species may be very simple or it may be extremely complex, the organism occurring under many different forms at different phases or periods of its development . The polymorphism of the Protozoa is best considered under three categories, according to the three See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main causes to which it is due, namely, first, polymorphism due to See also:

• ADAPTATION (from Lat. adaptare. to fit to)

adaptation to different conditions of existence; secondly, polymorphism due to See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences of size and structure during growth; thirdly, polymorphism due to the differentiation of individuals in connexion with the process of syngamy or sexual conjugation . x . Polymorphism in Relation to Life-conditions.—As a protection against unfavourable conditions, or for other reasons, most Protozoa have the See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of passing into a resting condition, during which the vital functions may be wholly or in part suspended . In the resting phase the animal usually becomes enveloped in a resistant membrane or cyst secreted by it, and is then said to be encysted . The formation of a cyst may be a response to conditions of various kinds .

Very commonly it is formed to protect the organism against a See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change of medium, as in the case of See also:

• FRESHWATER

freshwater forms liable to See also:

• DESICCATION (from the Lat. desiccare, to dry up)

desiccation, or of parasites about to pass out of the bodies of their hosts . In other cases the organism passes into the resting state in order 'to absorb ingested nutriment or in order to enter upon reproductive phases . As a preparation for encystment, organs of locomotion, if present, are retracted or cast off; contractile vacuoles cease to be formed; and the food-vacuoles disappear, usually by digestion of their contents and rejection of the waste residue . The body becomes rounded off and more or less spherical in form, and the protoplasm becomes denser, that is, less fluid and more opaque, but at the same See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time of diminished specific gravity, by loss of water . The cyst is then secreted at the surface as a layer of varying thickness and toughness . In the encysted condition many Protozoa are capable of being transported by the wind_ a fact which explains their appearance in infusions and. quids exposed to the air . In favourable conditions the cysts germinate, that is to say, the envelope is dissolved and the contained See also:

• ORGAN

organ-ism or organisms are set free to enter upon the strenuous life once more . In the Mycetozoa, organisms adapted to a semi-terrestrial life in moist surroundings, the protoplasm is capable, when desiccated, of passing into a tough condition resembling sealing-See also:

• WAX

wax, which, when moistened, assumes again its normal appearance and active condition . Resting phases, analogous to encystment, are seen in the spores of various forms, especially those of parasitic habit, which are commonly enclosed in tough, resistant envelopes or sporocysts, and enveloped as a protection against change of medium or of host . Within the sporocyst multiplication of the sporoplasm may take place to form more or fewer sporozoites . The sporocysts usually show definite symmetry and structure, infinitely variable in different species . In a suitable medium the spores germinate by rupture of the sporocysts and See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape of the contents .

2 . Polymorphism in Relation to Growth and Development.—In many species of Protozoa there is hardly any difference to be observed between different individuals during their active phases except in size . Those individuals about to multiply by fission are slightly above the normal in dimensions: op the other hand, those resulting from recent fission will be smaller than the See also:

• AVERAGE

average; and such differences are, it need hardly be said, more pronounced when the fission is of the unequal binary type, or in cases of gemmation or multiple fission . In cases also where a given See also:

• STRAIN (through O. Fr. straindre, estraindre, mod. i treindre, from Lat. stringere, to draw tight, related to stress, stretch, string, &c.)

strain of a species is becoming senile, it is sometimes observed that the individuals are markedly undersized on the average . On the other hand, it is often the case that the young individuals resulting from a recent act of multiplication may differ from adult individuals of the species, not merely in size, but in structural characters, to such an extent that their relationship to the adult forms could not be determined by simple inspection without other See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence . This is especially true of those species in which multiplication by sporulation occurs, giving rise to numerous small spores which may at first be in a resting condition, enveloped in protective sporocysts, but which sooner or later become free, motile individuals known technically as swarm-spores . Thus in many Sarcodina the adult is a large amoeboid organism which produces by sporulation a great number of relatively minute swarm-spores . These may be either, as in the common Amoeba See also:

• PROTEUS
• PROTEUS (Proteus anguinus)

proteus, amoeboid organisms, so-called amoebulae or pseudopodiospores, or, as in the Foraminifera and Radiolaria, flagellated organisms, so-called flagellulae or flagellispores . Sometimes, as in many Mycetozoa, amoeboid and flagellated phases may succeed each See also:

• ETHER, (C2H5)2O

ether rapidly in the development of the swarm-spores . The See also:

• FAMILIAR (through the Fr. familier, from Lat. familiaris, of or belonging to the familia, family)

familiar Noctiluca miliaris is another instance of a species which produces by sporulation numerous tiny swarm-spores quite different from the parent form in their characters . Such instances could be multiplied indefinitely amongst the Protozoa . When the young individuals differ greatly from the adults in structure and appearance they may be regarded as larval forms, and it is interesting to See also:

• NOTE
• NOTE (Lat. nota, mark, sign, from noscere, to know)

note that such forms appear to be just as much recapitulative, in the phylogenetic sense, as are the larvae of many Metazoa .

A striking instance is that of the Acinetaria, in which the swarm-spores produced by gemmation are ciliated, and thus betray See also:

• AFFINITIES

affinities with the Ciliata which could hardly be suspected from a study of the adult forms alone . Similarly, in the genus Trypanosoma, the young forms often show a Herpetomonas-like structure which is probably of phyletic significance . The swarm-spores of Sarcodina and of Noctiluca mentioned above can, perhaps, be regarded in the same light . On the other hand, many larval forms cannot be considered as exhibiting recapitulative characters, but merely as adaptations to environment or other special life-conditions . This is especially true, as in Metazoa, of parasitic forms, subject as they are to great vicissitudes, to See also:

• COPE
• COPE (M.E. cape, cope, from Med. Lat. capa, cappa)
• COPE, EDWARD DRINKER (1840-1897)
• COPE, EDWARD MEREDITH (1818-1873)

cope with which the most finely adjusted adaptations are necessary on the part of the organism . 3 . Polymorphism in Relation to See also:

• SEX (Lat. sexes; possibly connected with secure, to cut)

Sex.—In all Protozoa of which the life-cycle has been made known in its entire course, a process of syngamy or sexual union has been found to occur . There are still many forms in which syngamy remains to be discovered: this is true even of some See also:

• GROUPS
• GROUPS, THEORY

groups of considerable extent . It is quite possible, therefore, that Protozoa exist in which syngamy does not occur . In view, however, of the widespread occurrence of sexual processes amongst unicellular organisms, both of animal and vegetable nature, and the fact that extended observation continually brings to light new instances of this kind, it is safer, in cases amongst the Protozoa in which syngamy is not known to occur, to explain its apparent absence by the imperfections of the present state of our know-ledge, than to suppose that in such forms sexual phenomena are entirely lacking in the life-cycle.' The process of syngamy, though greatly diversified in different forms, consists essentially of one and the same process in all cases; namely, the fusion of nuclear matter from two distinct individuals . Plus ca change, plus c'est la mgme See also:

• CHOSE (Fr. for " thing ")