ARTHROPODA  , a name, denoting the See also:

• POSSESSION
• POSSESSION (Lat. possessio, possidere, to possess)

possession by certain animals of jointed limbs, now applied to one of the three sub-phyla into which one of the See also:

• GREAT

great phyla (or See also:

• PRIMARY

primary branches) of coelomocoelous animals—the See also:

• APPENDICULATA

Appendiculata—is divided; the other two being respectively the See also:

• CHAETOPODA (Gr. xairq, hair, aous, foot)

Chaetopoda and the See also:

• ROTIFERA (or ROTATORIA)

Rotifera . The word "Arthropoda " was first used in See also:

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

classification by See also:

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

Siebold and Stannius (Lehrbuch der vergleich . Anatomic, See also:

• BERLIN
• BERLIN, CONGRESS AND TREATY OF
• BERLIN, ISAIAH (1725–1799)

Berlin, 1845) as that of a primary See also:

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

division of animals, the others recognized in that See also:

• TREATISE

treatise being See also:

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

Protozoa, Zoophyta, Vermes, See also:

• MOLLUSCA

Mollusca and See also:

• VERTEBRATA

Vertebrata . The names Condylopoda and See also:

• GNATHOPODA

Gnathopoda have been subsequently proposed for the same See also:

• GROUP

group . The word refers to the jointing of the chitinized exo-See also:

• SKELETON

skeleton of the limbs or lateral appendages of the animals included, which are, roughly speaking, the See also:

• CRUSTACEA

Crustacea, See also:

• ARACHNIDA

Arachnida, See also:

• HEXAPODA (Gr. 4, six, and gobs, foot)

Hexapoda (so-called " true See also:

• INSECTS

insects "), Centipedes and Millipedes . This primary group was set up to indicate the residuum of See also:

• CUVIER, GEORGES LEOPOLD CHRETIEN FREDERIC DAGOBERT, BARON (1769-1832)

Cuvier's See also:

• ARTICULATA

Articulata when his class Annelides (the See also:

• MODERN

modern Chaetopoda) was removed from that embranchement . 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 C . T . E. von Siebold and H . Stannius renovated the group Vermes of See also:

• LINNAEUS

Linnaeus, and placed in it the Chaetopods and the parasitic See also:

• WORMS

worms of Cuvier, besides the Rotifers and Turbellarian worms .l The result of the knowledge gained in the last See also:

• QUARTER (through Fr. from Lat. quartarius, fourth part)

quarter of the loth See also:

• CENTURY (from Lat. centuria, a division of a hundred men)

century has been to discredit altogether the group Vermes (see See also:

• WORM

WoRM), thus set up and so largely accepted by See also:

• GERMAN
• GERMAN, DUTCH AND SCANDINAVIAN

German writers even at the See also:

• PRESENT

present See also:

• DAY (O. Eng. dreg, Ger. Tag; according to the New English Dictionary, " in no way related to the Lat. dies")
• DAY, JOHN (1574-1640?)
• DAY, THOMAS (1748-1789)

day . We have, in fact, returned very nearly to Cuvier's conception of a great division or See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch, which he called Articulata, including the Arthropoda and the Chaetopoda (Annelides of See also:

• LAMARCK,

Lamarck, a name adopted by Cuvier), and differing from it only by the inclusion of the Rotifera . The name Articulata, introduced by Cuvier, has not been retained by subsequent writers .

The same, or nearly the same, assemblage of animals has been called Entomozoaria by de See also:

• BLAINVILLE
• BLAINVILLE, HENRI MARIE DUCROTAY DE (1777–1850)

Blainville (1822), Arthrozoa by Burmeister (1843), Entomozoa or Annellata by H . Milne-See also:

• EDWARDS, AMELIA ANN BLANDFORD (1831-1892)
• EDWARDS, BELA BATES (18o2-1852)
• EDWARDS, BRYAN (1743–1800)
• EDWARDS, GEORGE (1693–1773)
• EDWARDS, HENRY THOMAS (1837–1884)
• EDWARDS, JONATHAN (1703—1758)
• EDWARDS, LEWIS (1806–1887 )
• EDWARDS, RICHARD (c. 1523–1566)
• EDWARDS, T
• EDWARDS, THOMAS CHARLES (1837–1900)

Edwards (1855), and Annulosa by See also:

• ALEXANDER
• ALEXANDER (1461-1506)
• ALEXANDER (ALEXANDER OF BATTENBERG) (1857-1893)
• ALEXANDER (ALEXANDER OsxENOVici) (1876-1903)
• ALEXANDER, ARCHIBALD (1772—1851)
• ALEXANDER, FRANCIS (1800—1881)
• ALEXANDER, GEORGE (1858— )
• ALEXANDER, JOHN WHITE (1856- )
• ALEXANDER, JOSEPH ADDISON (18o9—186o)
• ALEXANDER, SIR JAMES EDWARD (1803—1885)
• ALEXANDER, WILLIAM (1824— )
• ALEXANDER, WILLIAM LINDSAY (1808—1884)

Alexander M`Leay (1819), who was followed by See also:

• HUXLEY, THOMAS HENRY (1825–1895)

Huxley (1856) . The See also:

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

character pointed to by all these terms is that of a 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 segmentation of the See also:

• BODY

body . This, however, is not the character to which we now ascribe the See also:

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

chief See also:

• WEIGHT

weight as See also:

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

evidence of the genetic See also:

• AFFINITY (Lat. affinitas, relationship by marriage, from offinis, bordering on, related to; finis, border, boundary)
• AFFINITY, CHEMICAL

affinity and monophyletic (uni-ancestral) origin of the Chaetopods, Rotifers and Arthropods . It is the existence in each ring of the body of a pair of hollow lateral appendages or parapodia, moved by See also:

• INTRINSIC (through Fr. intrinsique, from Lat. intrinsecus, inwardly; inter, within, secus, following, from root of sequi, to follow)

intrinsic muscles and penetrated by See also:

• BLOOD

blood-spaces, which is the leading fact indicating the See also:

• AFFINITIES

affinities of these great sub-phyla, and uniting them as blood-relations . The 1 The group Arthropoda itself,th usconstituted,was precisely iden tical in its See also:

• AREA

area with the Insecta of Linnaeus, the Entoma of See also:

• ARISTOTLE
• ARISTOTLE (384-322 B.C.)

Aristotle . But the word " See also:

• INSECT

Insect " had become limited since the days of Linnaeus to the Hexapod Pterygote forms, to the exclusion of his See also:

• APTERA (Greek for " wingless ")

Aptera . Lamarck's penetrating See also:

• GENIUS (from Lat. genere, gignere)

genius is chiefly responsible for the shrinkage of the word Insecta, since it was he who, See also:

• FORTY

forty years after Linnaeus 's See also:

• DEATH

death, set up and named the two great classes Crustacea and Arachnida (included by Linnaeus under Insecta as 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 " Aptera "), assigning to them equal See also:

• RANK (O.Fr. rant or rent, mod. rang, generally connected with the O.E. and O.H.G. bring, a ring)

rank with the remaining Insecta of Linnaeus, for which he proposed the very appropriate class-name " Hexapoda." Lamarck, however, appears not to have insisted on this name Hexapoda, and so the class of Pterygote Hexapods came to retain the group-name Insecta, which is, historically or etymologically, no more appropriate to them than it is to the classes Crustacea and Arachnida . The tendency to retain the See also:

• ORIGINAL

original name of an old and comprehensive group for one of the fragments into which such group becomes divided by the advance of knowledge—instead of keeping the name for its logical use as'a comprehensive See also:

• TERM

term, including the new divisions, each duly provided with a new name—is most curiously illustrated in the See also:

• HISTORY

history of the word See also:

• PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

physiology . See also:

• CICERO

Cicero says, " Physiologia naturae ratio," and such was the meaning of the name See also:

• PHYSIOLOGUS

Physiologus, given to a cyclopaedia of what was known and imagined about See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth, See also:

• SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain)
• SEA, COMMAND OF THE

sea, See also:

• SKY (M. Eng. skie, cloud; O. Eng. skua, shade; connected with an Indo-European root sku, cover, whence " scum," Lat. obscurus, dark, &c.)

sky, birds, beasts and fishes, which for a thousand years was the authoritative source of See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information on these matters, and was translated into every See also:

• EUROPEAN

European See also:

• TONGUE (O. Eng. lunge)

tongue . With the revival of learning, however, first one and then another See also:

• SPECIAL

special study became recognized—See also:

• ANATOMY
• ANATOMY (Gr. avaroyil, from ava-silo c', to cut up)

anatomy, See also:

• BOTANY (from Gr. l3or6v17, plant; ,66vicety, to graze)

botany, See also:

• ZOOLOGY (from Gr. Nov, a living thing, and ?byos, theory)

zoology, See also:

• MINERALOGY

mineralogy, until at last the great comprehensive term physiology was bereft of all its once-included subject-See also:

• MATTER

matter, excepting the study of vital processes pursued by the more learned members of the medical profession . Professional tradition and an astute See also:

• PERCEPTION (from Lat. percipere, to perceive)

perception on their See also:

• PART

part of the omniscience suggested by the terms, have See also:

• LEFT

left the medical men in See also:

• ENGLISH

English-speaking lands in undisturbed but illogical possession of the words physiology, physic and physician .

II Periodical and commercial . :.22 parapodia (fig . 8) of the marine branchiate worms are the same things genetically as the " legs " of Crustacea and Insects (See also:

• FIGS

figs. lo and II) . Hence the term Appendiculata was introduced by Lankester (See also:

• PREFACE (Med. Lat. prefatia, for classical praefatio, praefari, to speak beforehand)

preface to the English edition of See also:

• GEGENBAUR, CARL (1826-1903)

Gegenbaur's See also:

• COMPARATIVE

Comparative Anatomy, 1878 ) to indicate the group . The relation-See also:

• SHIPS

ships of the Arthropoda thus stated are shown in the subjoined table: S Sub-phylum r . Rotifera . Phylum—APPENDICULATA 2 . Chaetopoda . 3 . Arthropoda . The ROTIFERA are characterized by the retention of what appears in Molluscs and Chaetopods as an embryonic See also:

• ORGAN

organ, the velum or ciliated prae-oral See also:

• GIRDLE (O. Eng. gyrdel, from gyrdan, to gird; cf. Ger. Gurtel, Dutch gordel, from giirten and gorden; "gird" and its doublet " girth " together with the other Teutonic cognates have been referred by some to the root ghar—to seize, enclose, seen in Gr. )(s

girdle, as a locomotor and 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-seizing apparatus, and by the reduction of the See also:

• MUSCULAR

muscular parapodia to a rudimentary or non-existent See also:

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

condition in all present surviving forms except Pedalion . In many important respects they are degenerate—reduced both in See also:

• SIZE

size and elaboration of structure .

The CHAETOPODA are characterized by the possession of horny epidermic chaetae embedded in the integument and moved by muscles . Probably the chaetae preceded the development of parapodia, and by their concentration and that of the muscular bundles connected with them at the sides of each segment, led directly to the See also:

• EVOLUTION

evolution of the parapodia . The parapodia of Chaetopoda are never coated with dense chitin, and are, therefore, never converted into jaws; the See also:

• PRIMITIVE

primitive " See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

head-See also:

• LOBE

lobe " or prostomium persists, and frequently carries eyes and sensory tentacles . Further, in all members of the sub-phylum Chaetopoda the relative position of the prostomium, mouth and peristomium or first ring of the body, retains its primitive character . We do not find in Chaetopoda that parapodia, belonging to primitively See also:

• POST

post-oral rings or body-segments (called " somites," as proposed by H . Milne-Edwards), pass in front of the mouth by adaptational shifting of the oral See also:

• APERTURE (from Lat. aperire, to open)

aperture . (See, however, 8.) The ARTHROPODA might be better called the " Gnathopoda," since their distinctive character is, that one or more pairs of appendages behind the mouth are densely chitinized and turned (See also:

• FELLOW

fellow to fellow on opposite sides) towards one another so as to See also:

• ACT (Lat. actus, actum)

act as jaws . This is facilitated by an important See also:

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

general 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 in the position of the parapodia; their basal attachments are all more ventral in position than in the Chaetopoda, and tend to approach from the two sides towards the See also:

• MID

mid-ventral See also:

• LINE

line . Very usually (but not in the Onychophora = See also:

• PERIPATUS

Peripatus) all the parapodia are plated with chitin secreted by the epidermis, and divided into a See also:

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

series of See also:

• JOINTS

joints—giving the " arthropodous or hinged character . There are other remarkable and distinctive features of structure which hold the Arthropoda together, and render it impossible to conceive of them as having a polyphyletic origin, that is to say, as having originated separately by two or three distinct lines of descent from See also:

• LOWER

lower animals; and, on the contrary, establish the view that they have been See also:

• DEVELOPED

developed from a single line of primitive Gnathopods which arose by modification of parapodiate annulate worms not very unlike some of the existing Chaetopods . These additional features are the following—(I) All existing Arthropoda have an ostiate See also:

• HEART
• HEART, LUNG

heart and have undergone " phleboedesis," that is to say, the peripheral portions of the blood-vascular See also:

• SYSTEM

system are not See also:

• FINE

fine tubes as they are in the Chaetopoda and as they were in the hypothetical ancestors of Arthropoda, but are swollen so as to obliterate to a large extent the coelom, whilst the See also:

• SEPARATE

separate See also:

• VEINS

veins entering the dorsal See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel or heart have coalesced, leaving valvate See also:

• OSTIA

ostia (see fig . I) by which the blood passes from a pericardial blood-sinus formed by the fused veins into the dorsal vessel or heart (see Lankester's Zoology, part ii., See also:

• INTRODUCTORY

introductory See also:

• CHAPTER (a shortened form of chapiter, a word still used in architecture for a capital; derived from O. Fr. chapitre, Lat. capitellum, diminutive of caput, head)

chapter, 1900) .

The only exception to this is in the See also:

• CASE
• CASE, JOHN (d. 1600)

case of See also:

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

minute degenerate forms where the heart has disappeared altogether . The rigidity of the integument caused by the deposition of dense chitin upon it is intimately connected with the physiological activity and See also:

• FORM (Lat. forma)

form of all the See also:

• INTERNAL

internal See also:

• ORGANS

organs, and is undoubtedly correlated with the See also:

• TOTAL

total disappearance of the circular muscular layer of 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 present in Chaetopods . (2) In all existing Arthropoda the region in front of the mouth is no longer formed by the primitive prostomium or head-lobe, butone or more segments, originally post-oral, with their appendages have passed in front of the mouth (prosthomeres) . At the same time the prostomium and its appendages cease to be recognizable as distinct elements of the head . The See also:

• BRAIN (A.S. braegen)

brain no longer consists solely of the See also:

• NERVE (Lat. nervus, Gr. vevpov, a bowstring)

nerve-ganglion-See also:

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

mass proper to the prostomial lobe, as in Chaetopoda, but is a composite (syncerebrum) produced by the See also:

• FUSION

fusion of this and the nerve-ganglion-masses proper to the prosthomeres or segments which pass forwards, whilst their parapodia (= appendages) become converted into See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye-stalks, and antennae, or more rarely grasping organs . (3) As in Chaetopoda, coelomic funnels (coelomoducts) may occur right and left /~ < k, k See also:

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

ray . NK 11 C li (`C raw-- 11 C ---'-A V V r After Lankester, Q . J . Mic . Sti. vol. xxxiv., 1£93 . as pairs in each ring-like segment or somite of the body, and some of these are in all cases retained as gonoducts and often as renal excretory organs (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 glands, coxal glands of Arachnida, not crural glands, which are epidermal in origin); but true nephridia, genetically identical with the nephridia of earthworms, do not occur (on the subject of coelom, coelomoducts and nephridia, see the introductory chapter of part ii. of Lankester's Treatise on Zoology) . See also:

• TABULAR

Tabular Statement of the Grades, Classes and Sub-classes of the Arthropoda.—It will be convenient now to give in the clearest form a statement of the larger subdivisions of the Arthropoda which it seems necessary to recognize at the present day .

The See also:

• JUSTIFICATION

justification of the arrangement adopted will form the substance of the See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest of the present See also:

• ARTICLE (from Lat. articulus, a joint)

article . The orders included in the various classes are not discussed here, but are treated of under the following titles:—PERIPATUS (Ontychophora), See also:

• CENTIPEDE

CENTIPEDE and See also:

• MILLIPEDE

MILLIPEDE (See also:

• MYRIAPODA (Gr. for " many-legged ")

Myriapoda), HEXAPODA (Insecta), ARACHNIDA and CRUSTACEA . See also:

• SUS

Sus-PHYLTm ARTHROPODA (of the Phylum Appetdiculata) . Grade A . Hyparthropoda (hypothetical forms connecting ancestors of Chaetopoda with those of Arthropoda) . Grade B . Protarthropoda . Class ONYCHOPHORA . Ex.—Peripatus . Grade C . Euarthropoda . Class I .

DIPLOPODA . Ex.—Julus . Class 2 . ARACHNIDA . Grade a . Anomomeristica . Ex.—Phacops . Grade b . Nomomeristica . (a) Pantopoda . Ex.—Pycnogonum . (b) Euarachnida .

Ex.—Limulus, See also:

• SCORPIO ("THE SCORPION")

Scorpio, Mygale, See also:

• ACARUS (from Gr. a.Kapc, a mite)

Acarus . Class 3 . CRUSTACEA . Grade a . See also:

• ENTOMOSTRACA

Entomostraca . Ex . Apus, Branchipus, Cyclops, Balanus . Grade b . See also:

• MALACOSTRACA

Malacostraca . Ex.—Nebalia, Astacus, Oniscus, Gammarus . Class 4 . CHILOPODA .

Ex.—Scolopendra . Class 5 . HEXAPODA (syn . Insecta Pterygota) . Ex.—Locusta, Phryganea, Papilio, See also:

• APIS

Apis, Musca, Cimex, Lucanus, Machilis . Incertae sedis—See also:

• TARDIGRADA

Tardigrada, Pentastomidae (degenerate forms) . The Segmentation of the Body of Arthropoda.—The body of the Arthropoda is more or less clearly divided into a series of rings, segments, or somites which can be shown to be repetitions one of another, possessing identical parts and organs which may be larger or smaller, modified in shape or altogether suppressed in one somite as compared with another . A similar constitution of the body is more clearly seen in the Chaetopod worms . In the Vertebrata also a repetition of See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units of structure (myotomes, vertebrae, &c.)—which is essentially of the same nature as the repetition in Arthropods and Chaetopods, but in many respects subject to See also:

• PECULIAR

peculiar developments—is observed . The name "See also:

• METAMERISM (Gr. writ, after, µEpos, a part)

metamerism " has been given to this structural phenomenon because the " See also:

• MERES, FRANCIS (1565-1647)

meres," or repeated units, follow one another in line . Each such " See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere is often called a metamere." A satisfactory 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 of the structure of the Arthropods demands a knowledge of what may be called the See also:

• LAWS

laws of metamerism, and reference should be made to the article under that head . The Theory of the Arthropod Head.—The Arthropod head is a tagma or group of somites which differ in number and in their relative position in regard to the mouth, in different classes .

In a See also:

• SIMPLE

simple Chaetopod (fig . 2) the head consists of the first somite only; that somite is perforated by the mouth, and is provided with a prostomium or prae-oral lobe . The prostomium is essentially a part or outgrowth of the first somite, and cannot be regarded as itself a somite . It gives rise to a nerve-ganglion mass, the prostomial ganglion . In the marine Chaetopods (the See also:

• POLYCHAETA

Polychaeta) (fig . 3), we -find the same essential structure, but the prostomium may give rise to two or more tactile tentacles, From Goo lrich, M:c, . and to the vesicular eyes . The somites have Q . vol. xi, p .. 24 . 1;. well-marked parapodia, and the second and jacent region of an Oli- thus contribute to form " the head." But gochaet Chaetopod. the mouth remains as an inpushing of the Pr, The prostomium. wall of the first somite . m, The mouth .

The Arthropoda are all distinguished from A, The prostomial the C.haetopoda by the fact that the head ganglion-mass or consists of one or more somites which See also:

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

lie in archi-cerebrum. front of the mouth (now called prosthomeres), I, II, III, coelom of as well as of one or more somites behind it the first, second (opisthomeres) . The first of the post-oral and third somites. somites invariably has its parapodia modi- fied so as to form a pair of hemignaths (mandibles) . About 187o the question arose for discussion whether the somites in front of the mouth are to be considered as derived from the prostomium of a Chaetopod-like ancestor . Milne-Edwards and Huxley had satisfied themselves with discussing and establishing, according to the data at their command, the number of somites in the Arthropod head, but had not considered the question of the nature of the prae-oral somites . Lankester (2) was the first to suggest that (as is actually the fact in the Nauplius larva of the Crustacea) the prae-oral somites or prosthomeres and their appendages were ancestrally post- oral, but have become prae-oral " by adaptational shifting of the oral aperture." This has proved to be a See also:

• SOUND
• SOUND, THE (Danish Oresund)

sound See also:

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

hypothesis and is now accepted as the basis upon which the Arthropod head must be inter- preted (see Korschelt and Heider (3)) . Further, the morphologists of the 'fifties appear, with few exceptions, to have ac- cepted a preliminary See also:

• SCHEME (Lat. schema, Gr. oxfjya, figure, form, from the root axe, seen in exeiv, to have, hold, to be of such shape, form, &c.)

scheme with regard to the Arthropod head and Arthropod segmentation generally, which was mis- leading and caused them to adopt forced conclusions and interpretations . It was FIG . 3.— See also:

• DIAGRAM

Diagram of conceived by Huxley, among others, that the head and adjacent the same number of cephalic somites region of a Polychaet would be found to be characteristic of all Chaetopod . Letters as the diverse classes of Arthropoda, and that in fig . 1, with the addi- the somites, not only of the head but of tion of T, prostomial the various regions of the body, could tentacle; Pa, parapo- be closely compared in their numerical dium . (From See also:

• GOODRICH, or GOODRICKE, THOMAS (d. 1554)
• GOODRICH, SAMUEL GRISWOLD (1793-1860)

Goodrich.) sequence in classes so distinct as the Hexapods, Crustaceans and Arachnids . The view which it now appears necessary to take is, on the contrary, this—viz. that all the Arthropoda are to be traced to a See also:

• COMMON

common ancestor resembling a Chaetopod worm, but differing from it in having lost its chaetae and in having a prosthomere in front of the mouth (instead of prostomium only) and a pair of hemignaths (mandibles) on the parapodia of the buccal somite .

From this ancestor Arthropods with heads of varying degrees of complexity have been developed characteristic of the different classes, whilst the parapodia and somites of the body have become variously modified and grouped in these different classes . The resemblances which the members of one class often present to the members of another class in regard to the form of the See also:

• LIMB

limb-branches (rami) of the parapodia. and the formation of tagmata (regions) are nothastily to be ascribed to common See also:

• INHERITANCE

inheritance, but we must consider whether they are not due to homoplasy—that is, to the moulding of natural selection acting in the different classes upon fairly similar elements under like exigencies . The'structure of the head in Arthropods presents three profoundly separated grades of structure dependent upon the number of prosthomeres which have been assimilated by the prae-oral region . The classes presenting these distinct plans of head-structure cannot be closely associated in any scheme of classification professing to be natural . Peripatus, the type-genus of the class Onychophora, stands at the See also:

• BASE

base of the series with only a single prosthomere (fig . 4) . In Peripatus the prostomium of the Chaetopod-like ancestor is atrophied, but it is possible that two processes on the front of the head (FP) represent in the embryo the dwindled prostomial tentacles . The single prosthomere carries the retractile tentacles as its "parapodia." The second somite is the buccal somite (II, fig . 4) ; its parapodia have horny jaws on their ends, like the claws FIG 4.—Diagram of the head on the following legs (fig . 9), and and adjacent region of Periact as hemignaths (mandibles) . The patus . Monoprosthomerous. study of sections of the embryo m, Mouth .

establishes these facts beyond doubt . I, Coelom of the first somite It also shows us that the neuro- which carries the anten- meres, no less than the embryonic nae and is in front of the coelomic cavities, point to the exist- mouth . once of one, and only one, prostho- II, Coelom of the second mere in Peripatus, of which the somite which carries the protocerebrum," P, is the neuro- mandibles (hence deu- mere, whilst the deuterocerebrum, terognathous) . D, is the neuromere of the second III and IV, Coelom of the third or buccal somite . A brief indication and See also:

• FOURTH

fourth somites. of these facts is given by saying FP, Rudimentary frontal See also:

• PRO

pro- that the Onychophora are " deuter- cesses perhaps repre- ognathous "—that is to say, that senting the prostomial the buccal somite carrying the See also:

• MAN
• MAN, ISLE OF (anc. Mona)

man- tentacles of Polychaeta. dibular hemignaths is the second of See also:

• ANT
• ANT (O. Eng. aemete, from Teutonic a, privative, and maitan, cut or bite off, i.e. " the biter off "; aemete in Middle English became differentiated in dialect use to (mete, then amte, and so ant, and also to emete, whence the synonym " emmet," now only u

Ant, Antenna or tactile ten- the whole series. tacle . What has become of the nerve- Md, Mandible . ganglion of the prostomial lobe of Op, Oral-papilla . the Chaetopod in Peripatus is not P, Protocerebrum or fore- clearly ascertained, nor is its See also:

• FATE

fate most cerebral mass be- indicated by the study of the em- longing to the first bryonic head of other Arthropods so somite . far . Probably it is fused with the D, Deuterocerebrum, consist- protocerebrum, and may also be See also:

• ING

ing of ganglion cells be- concerned in the history of the very longing to the second or peculiar paired eyes of Peripatus, mandibular somite . which are like those of Chaetopods in (After Goodrich.) structure—viz.vesicles with an intravesicular See also:

• LENS
• LENS (from Lat. lens, lentil, on account of the similarity of the form of a lens to that of a lentil seed)

lens, whereas the eyes of all other Arthropodshaveessentiallyanother structure, being " cups " of the epidermis, in which a knob-like or See also:

• ROD (O.E. rodd, probably related to Norw. rudda, stick, rodda, stake)
• ROD, EDOUARD (1857-1910)

rod-like thickening of the cuticle is fitted as refractive See also:

• MEDIUM

medium . In Diplopoda (Julus, &c.) the results of embryological study point to a See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition of the front part of the head exactly similar to that which we find in Onychophora .

They are deuterognathous . The Arachnida present the first See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage of progress . Here See also:

• EMBRYOLOGY

embryology shows that there are two prosthomeres (fig . 5), and that the gnathobases of the chelae which act as the first pair of hemignaths are carried by the third somite . The Arachnida are therefore tritognathous . The two prosthomeres are indicated by their coelomic cavities in the embryo (I and II, fig . 5), and by two neuromeres, the protocerebrum and the deuterocerebrum . The appendages of the first prosthomere are not present as tentacles, as in Peripatus and Diplopods, but are possibly represented by the eyes or possibly altogether aborted . The appendages of the second prosthomere are the well-known chelicerae of the Arach- nids, rarely, if ever, antenniform, but modified as " retroverts"or clasp-See also:

• KNIFE (0. E. cuff, a word appearing in different forms in many Teutonic languages, cf. Du. knijf, Ger. Kneif, a shoe-maker's knife, Swed. knif; the ultimate origin is unknown; Skeat finds the origin in the root of " nip," formerly " knip "; Fr. canif is a

knife fangs in See also:

• SPIDERS

spiders . Fie . 5.—Diagram of the head and adjacent region of an Arachnid . Diprosthomerous in the adult condition, though embryologically the append-ages of somite II and the somite itself are, as here See also:

• DRAWN

drawn, not actually in front of the mouth .

E, Lateral eye . Ch . Chelicera . m, Mouth . P, Protocerebrum . D, Deuterocerebrum . I, II III, IV . Coelom of the first, second, third and fourth somites . (After Goodrich.) The Crustacea (fig . 6) and' the Hexapoda (fig . 7) agree in having three somites in front of the mouth, and it is probable, though not ascertained, that the Chilopoda (Scolopendra, &e.) are in the same case . The three ,prosthomeres or prae-oral somites of Crustacea due to the sinking back of the mouth one somite farther than in Arachnida See also:

• ATE

ate'not clearly indicated by coelomic cavities in the embryo, but their existence is clearly established by the development and position of the appendages arid by the neuromeres .

The eyes in some Crustacea are mounted on articulated stalks, and from the fact that they can after injury be replaced by antenna-like; appendages it is inferred that they represent the parapodia of the See also:

• MAST (2) (Anglo-Saxon maest, food, common to some Teutonic languages, and ultimately connected with " meat")
• MAST (I) (O. Eng. maest; a common Teutonic word, cognate with Lat. malus; from the medieval latinized form mast us comes Fr. malt)

Mast anterior prosthomere . The second prosthomere carries the 'first pair of antennae and the third the second See also:

• FAIR

Fair of antennae . Sometimes the pair of appendages has not a merey tactile jointed See also:

• RAMUS, PETRUS, or PIERRE DE LA RAMEE (1515-1572)

ramus, but is converted into a claw or clasper . Three neuromeresa proto-, deutero-, and trito-cerebrum--corresponding to those three prosthomeres aresharply marked in the embryo . The fourth somite is that in which the mouth now opens, and which accordingly has its appendages converted into hemignathous mandibles . The Crustacea are tetartogndthous . The history of the development of the head has been carefully worked out in the Hexapod insects . As in Crustacea and Arachnida, Qnt' FP, Frontal processes (observed in Cirrhiped nauplius-larvae) probably representing the prostomial tentacles of Chaetopods: e, Eye . Ant', First pair of antennae . Ant', Second pair of anmd, Mandible . [tennae. mx', mx'; First and second pairs of maxillae . m, Mouth .

I, II, and III, The three prosthomeres . IV, V, VI, The three somites following the mouth . P, Proto.eerebrum . D, Deutetocerebrum . T, Tritocerebrum . (After Goodrich.) a first prosthomere is indicated by the paired eyes and the protocerebrum; the second prosthomere has a well-marked coelomic cadity, carries the antennae, and has the deuterocerebrum for its neuromere . The third prosthomere is i epresented by a well-marked pair of coelomic cavities and the tritocerebrum (III, fig . 7), but has no appendages . They appear to have aborted . The existence of this third prosthomere corresponding to the third prosthomere of the Crustacea is a strong See also:

• ARGUMENT

argument for the derivation of the Hexapoda, and with them the Chilopoda, from some offshoot of the Crustacean See also:

• STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem or class . The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth : they are tetartognathous . The See also:

• ADHESION (from Lat. adhaerere, to adhere)

adhesion of a greater or less number of somites to the buccal somite posteriorly (opisthomeres) is a matter of importance, but of See also:

• MINOR
• MINOR (Lat. for smaller, lesser)
• MINOR, ROBERT CRANNELL (1839-1904)

minor 'importance, in the theory and history of the Arthropod head .

In Peripatus no such adhesion or fusion occurs . In Diplopoda two opisthomeres—that is to say, one in addition to the buccal somiteare See also:

• UNITED

united by a fusion of their terga with the terga of the prosthomeres . Their appendages are. respectively the' mandibles and the gnathochilarium . In Arachnida the highest forms exhibit a fusion of the tergites of five post-oral somites to form one. continuous See also:

• CARAPACE (a Fr. word, from the Span. carapacho, a shield or armour)

carapace united with the terga of the two prosthomeres . The five pairs of appendages of the post-oral somites of the head or prosoma thus constituted all primitively carry gnathobasic projections on their coxal joints, which act as hemignaths : in the more specialized forms the mandibular gnathobases cease to develop . In Crustacea the fourth or mandibular somite never has less thanthe two following somites associated with it by'the See also:

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

adaptation of their appendages as jaws, and the See also:

• ANKYLOSIS, or ANCYYLOSIS (from Gr. ayKVXos, bent, crooked)

ankylosis of their terga with that of the prosthomeres . But in higher Crustacea the cephalic" tagma" is ,extended, and more somites are added to the fusion;' and their appendages adapted as jaws of a 'See also:

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

kind . The Hexapoda are not known to us in their earlier or more primi= tive manifestations; we only know them as 'possessed of a definite number of somites arranged in definite See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers in three' great . tagmata . The head shows two See also:

• JAW (Mid. Eng. jawe, jowe and geowe, O. Eng. cheowan, connected with " chaw " and " chew," and in form with " jowl ")

jaw-bearing somites besides the mandibular somite (V, VI, in fig . 7)-thus six in all (as in some Crustacea), including prosthomeres, all ankylosed by their terga to form a cephalic See also:

• SHIELD (0. Eng. scild, cf. Du. and Ger. Schild, Dan. Skjold; the origin is doubtful, but may be referred to the root seen in " shell " or " scale "; another suggestion connects it with Icel. skjalla, to clash, rattle; it is not connected with the Indo-Ger
• SHIELD, WILLIAM (1748—1829)

shield . There is, however, See also:

• GOOD, JOHN MASON (1764-1827)

good embryological evidence in some Hexapods of the existence: of a seventh somite, the supra-lingual, occurring between the somite of the mandibles and the somite of the first maxillae (4) . This segment is indicated embryologically by its paired coelomic cavities .

It is practically an excalated somite, having no existence in the adult . It is probably not a mere coincidence that the H'exapod, with its two rudimentary somites devoid of appendages, is thus found to possess twenty-one somites, including that which carries the anus, and that" this is also the number' present in the Malacostracous Crustacea, The Segmental' Lateral Appendages or Limbs of A'thropoda.—It has taken some time to obtain any general See also:

• ACCEPTANCE (Lat. acceptare, frequentative form of accipere, to receive)

acceptance of the view that the parapodia of the Chaetopoda and the limbs of Arthropoda are genetically identi- cal sttuctures; yet if we compare the parapodium of Tomopteris or of Phyliodoce with one of the foliaceous limbs of Branchipus or Apus, the correspond- ences of the two are ; , striking . An erroneous 1h view of the funda- Ax' See also:

• MENTAL

mental See also:

• MORPHOLOGY, (Gr. yopdsil, form)

morphology of the Crustacean limb, and consequently of that of other Arthropoda, came into favour owing to the acceptance of the highly' modified limbs of Astacus as typical . Ptotopodite, endopodite, exopodite, and epipodite were See also:

• CON

con- FIG . 8.--Diagrainof thesomite-appendage See also:

• SIDE
• SIDE (mod. Eski Adalia)

side red to be the or parapodiumof a Polychaet Chaetopod morphological units of The ohaetae are omitted.' the crustacean limb . Ax, The See also:

• AXIS (Lat. for " axle ")

axis . Lank e s t e r (5) h as nr.c, Neuropodial'cirrhus . shown (and his views nr.l', nr.l', Neuropodial lobes or endites. have been accepted by nt.e . Notopodial cirrhus . Professors Korschelt irlotoy odial lobes or exites . and Heider their The parapodium is represented with its treatise on Embryology) neural or ventral See also:

• SURFACE

surface uppermost. that the limb of the (Original) . lowest Crustacea, such as Apus, consists of a corm or axis which maybe jointed, and gives rise to outgrowths, either See also:

• LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf-like or filiform, on its inner and See also:

• OUTER

outer margins (endites and exites) .

Such a coat (see figs. to and r> ), with its outgrowths, maybe compared to the simple parapodia of Chaetopoda with cirthi and branchial lobe (fig . 8) . It•is by the.spe6ialization of two'" endites that the endopodite and exopodite of higher Crustacea are formed, whilst a flabelliform exite is the homogen or genetic See also:

• EQUIVALENT

equivalent of the eppipodite (see Lankester, " Observations and Reflections on A pt's Cancriformis," Q . Mier . Sci.) . The reduction of the outgrowth-bearing "corm " of' the' parapodium of either a Chaetopod or an Arthropod to a simple ,cylindrical stump, devoid of outgrowths, is brought about when See also:

• MECHANICAL

mechanical conditions favour such a shape . We see it in certain Chaetopods (e.g . Hesione) and in the Arthropod Peripatus (fig . 9) . The See also:

• CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion of the Arthropod's limb into a jaw, as a See also:

• RULE

rule, is effected by the development of any endite near its base into a hard, chitinized, and often toothed gnathobase (see figs. ro and rt, en') . It is not true that all the biting processes of the Arthropod limb are thus' produced'—See also:

• FOG

fog instance, the jaws of Peripatus are formed by the axis or corm itself, whilst the See also:

• POISON

poison-jaws of Chilopods, as also their maxillae, appear to be formed rather by the See also:

• APEX

apex or terminal region of the tames of the limb; but the opposing jaws (=hemignaths) of Crustacea, Arachnida and Hexa: poda are gnathobases, and not the axis or Corm . The endopodite' (corresponding to the fifth endite of the limb of Apus, see fig. io) becomes in Crustacea the "" walking See also:

• LEG
• LEG (a word of Scandinavian origin, from the Old Norwegian leggr, cf. Swed. lagg, Dan. laeg; the O. Eng. word was sceanca, shank)

leg " of the mid-region of the body; it becomes the pulp or jointed See also:

• PROCESS

process of anterior segments.; A second ramus, the " exopodite" often is also retained in the form' of a palp or feeler .

In Apus, as the figure shows, there are four of' these" antenna-like" palisor filaments on the first thoracic limb." A common modifioatiottof the chief ramus of the Arthropod pares= See also:

• PODIUM (Gr. lr66tov, diminutive of ?roils, foot)

podium is the 'theta or nipper formed by the See also:

• ELONGATION

elongation of the' penultimate See also:

• JOINT (through Fr. from Lat. junctum, jungere, to join)

joint of the ramus, so that' the last joint ' See also:

• WORKS

works on its e, Eye . ant, Antenna . md, Mandible . mx', First maxilla . mx', Second maxilla . m, Mouth . Region of the first or eye-bearing prosthomere . IT, Coelom of the second antenna-bearing prosthomere . mere devoid of appendages . IV, V, and VI, Coelom of the fourth, fifth and See also:

• SIXTH

sixth somites . P, Protocerebrum belonging to the first prosthomere . D, Deuterocerebrum belonging to the second prosthomere .

T, Tritocerebruin` belonging to the third prosthomere . (After Goodrich.) as, for instance, in the See also:

• LOBSTER (O.E. lopustre, lopystre, a corruption of Lat. locusta, lobster or other marine shell-fish; also a locust)

lobster's claw . Such chelate rami or limbbranchesare independently developed in Crustacea and inArachnida, and are carried by somites of the body which do not correspond in position in the two See also:

• GROUPS
• GROUPS, THEORY

groups . The range of modification of which the rami or limb-branches of the limbs of Arthropoda are capable is very large, and in allied orders or even families or genera we often find what is certainly the palp of the same appendage (as determined by numerical position of the segments) —in one case antenniform, in another chelate, in another pediform, and in another reduced to a mere stump or absent altogether . Very probably the See also:

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

power which the appendage of a given segment has of assuming the perfected form and proportions previously attained by the append-See also:

• AGE (Fr. age, through late Lat. aetaticum, from aetas)

age of another segment must be classed as an instance of " homoeosis," not only where such a change is obviously due to abnormal development or injury, but also where it constitutes a difference permanently established between allied orders or smaller groups, or between the two sexes . The most extreme disguise assumed by the Arthropod parapodium or appendage is that of becoming a mere stalk supporting an eye—a fact which did not obtain general See also:

• CREDENCE, or CREDENCE TABLE

credence until the experiments of cut- 9.— tieg off the eye-stalk of See also:

• PALAEMON, QUINTUS REMMIUS

Palaemon, pendages or parapodia of that a jointed antenna-like append-Peripalus• age was regenerated in its See also:

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

place . A, A walking leg; pt to p4, Since the eye-stalks of Podophthalthe characteristic " pads "; f, See also:

• MATE (a corruption of make, from O. Eng. gemaca, a " comrade ")
• MATE, or PARAGUAY TEA

mate Crustacea represent append-the See also:

• FOOT

foot; cl', at, the two ages, we are forced to the conclusion claws. that the sessile eyes of other B, An oral papilla, one of Crustacea, and of other Arthropoda the second pair of post-oral generally, indicate the position of appendages. appendages which have atrophied.' C, One of the first post-oral From what has been said, it is pair of appendages or man- apparent that wecannot,in attemptdibles; cl', el', the greatly ing to discover the affinities and enlarged claws . (Compare A.) divergences of the various forms of The appendages are repre- Arthropoda, attach a very high sented with the neural or phylogenetic value to thecoincidence ventral surface uppermost. or divergence in form of the ap-Original. pendages belonging to the somites compared with one another . The See also:

• PRINCIPAL

principal forms assumed by the Arthropod parapodium and its rami may be thus enumerated: (1) Axial corm well developed, unsegmented or with two to four segments; lateral endites and exites (rami) numerous and of various lengths (certain 6 limbs of lower n Crustacea) . (2) Corm, with See also:

• SHORT, FRANCIS JOB (1857– )

short unsegmented rami, forming a flattened foliaceous appendage, adapted to See also:

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

swimming and respiration (See also:

• TRUNK (Fr. tronc, Lat. truncus, cut off, maimed)

trunk-limbs of Phyllopods) . I, 2, The two segments of the axis . (3) Corm alone en', The gnathobase. developed; with en to en', The five following " endites." no endites or fl, The flabellum or anterior exite. exites, but pro- br, The bract or posterior exite. vided with ter- minal chitinous claws (See also:

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

ordinary leg of Peripatus), with terminal jaw See also:

• TEETH (O.E. Eel); plural of tooth, O.E. top)

teeth (jaw of Peripatus), or with See also:

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

blunt extremity (oral papilla of same) (see fig .

9) . ' H . Milne-Edwards, who was followed by Huxley, See also:

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

long ago formu- lated the conclusion that the eye-stalks of Crustacea are modified appendages, basing his argument on a specimen of Palinurus (figured in See also:

• BATESON (BATSON or BETSON), THOMAS

Bateson's See also:

• BOOK

book (1), in which the eye-stalk of one side is replaced by an antenniform palp . See also:

• HOFER, ANDREAS (1767-181o)

Hofer (6) in 1894 described a similar case in Astacus . - (4) Three of the rami of the primitive limb (endites 5 and 6, and exite I) specially developed as endopodite, exopodite, and epipodite—the first two often as See also:

• FIRM

firm and strongly chitinized, segmented, leg-like structures; the original axis or corm reduced to a basal piece, with or without a distinct gnathobase (endite 1)—typical tri-ramose limb of higher Crustacea . (5) One ramus (the endopodite) alone developed—the original axis or corm serving as its basal joint with or without gnathobase . This is the usual uni-ramose limb found in the various classes of Arthropoda . It varies as to the presence or See also:

• ABSENCE (Lat. absentia)

absence of the jaw• process and as to the stoutness of the segments of the ramus, their number (frequently six, plus the basal corm), and the modification of the See also:

• FREE

free end . This may be filiform or See also:

• BRUSH (from Fr. brosse, which, like the English word, means both the undergrowth of a wood and the instrument; if the word in both these meanings is ultimately the same, then the origin is from a bundle of brushwood used as a brush or broom, but this is h
• BRUSH, GEORGE DE FOREST (1855– )

brush-like or lamellate when it is an antenna or palp; a simple spike (walking leg of Crustacea, of other aquatic forms, and of Chilopods and Diplopods) ; the_terminal joint flattened (swimming leg of Crustacea and Gigantostraca) ; the terminal joint provided with two or with three recurved claws (walking leg of many terrestrial forms—e.g . Hexapoda and Arachnida) ; the penultimate joint with a process equal in length to the last joint, so as to form a nipping organ (chelae of Crustaceans and Arachnids) ; the last joint reflected and movable on the See also:

• PEN (Lat. penna, a feather, pen)

pen-ultimate, as the blade of a clasp-knife on its handle (the retrovert, After Lankester, Q . J . Mic .

Sci. vol. xxi., 1881 . the axis with muscular bands . Ent, Gnathobase . En' to En', The elongated jointed endites (rami) . En', The rudimentary sixth endite (exopodite of higher Crustacea) . Fl, The flabellum which becomes the epipodite of higher forms . Br, The bract devoid of muscles and See also:

• RESPIRATORY

respiratory in See also:

• FUNCTION

function . toothed so as to act as a biting jaw in the Hexapod See also:

• MANTIS

Mantis, the Crustacean Squilla and others) ; with the last joint produced into a See also:

• NEEDLE (O. Eng. ncedl; the word appears in various forms in Teutonic languages, Ger. Nadel, Dutch naal, the root being ne-, to sew, cf. Ger. nahen, and probably Lat. nere, to spin, Gr. vi)ats, spinning)

needle-like stabbing process in spiders . (6) Two rami developed (usually, but perhaps not always, the equivalents of the endopodite and exopodite) supported on the somewhat elongated corm (basal segment) . This is the typical " bi-ramose limb " often found in Crustacea . The rami may be flattened for swimming, when it is " a bi-ramose swimmeret," or both or only one may be filiform and finely annulate; this is the form often presented by the antennae of Crustacea, and rarely by prae-oral appendages in other Arthropods . (7) The endopoditic ramus is greatly enlarged and flattened, without or with only one jointing, the corm (basal segment) is evanescent; often the See also:

• PLATE

plate-like endopodites of a pair of such appendages unite in the See also:

• MIDDLE

middle line with one another or by the intermediary of a sternal up-growth and form a single broad plate .

These are the plate-like swimmerets and opercula of Gigantostraca and Limulus among Arachnids and of Isopod Crustaceans . They may have rudimentary exopodites, and may or may not have branchial filaments or lamellae developed on their posterior faces . The simplest form to which they may be reduced is seen in the genital operculum of the See also:

• SCORPION (Lat. Scorpio)

scorpion . (8) The gnathobase becomes greatly enlarged and not separated by a joint from the corm; it acts as a hemignath or See also:

• HALF

half jaw working against its fellow of the opposite side . The endopodite may be retained as a small segmented palp at the side of the gnathobase or disappear (mandible of Crustacea, Chilopoda and Hexapoda) . (9) The corm becomes the seat of a development of a special visual organ, the Arthropod eye (as opposed to the Chaetopod eye) .. Its jointing (segmentation) may be retained, but its rami disappear (Podophthalmous Crustacea) . Usually it becomes atrophied, leaving the eye as a sessile organ upon the prae-oral region of the body . en en 2 . After Lankester, Q . J . Mic .

Sci. vol. xxi., r88r . (the eye-stalk and sessile lateral eyes of Arthropoda generally, exclusive of Peripatus) . (to) The forms assumed by special modification of the elements of the parapodium in the maxillae, labium, &c., of Hexapods, Chilopods, Diplopods, and of various .Crustacea, deserve special enumeration, but cannot be dealt with without ample space and See also:

• ILLUSTRATION

illustration . It may be pointed out that the most See also:

• RADICAL (Lat. radix, a root)

radical difference presented in this See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list is that between appendages consisting of the corm alone without rami (Onychophora) and those with more or less developed rami (the rest of the Arthropoda) . In the latter class we- should distinguish three phases: (a) those with numerous and comparatively undeveloped rami; (b) those with three, or two highly developed rami, or with only one—the corm being reduced to the dimensions of a mere basal segment; (c) those reduced to a secondary simplicity (degeneration) by overwhelming development of one segment (e.g. the isolated gnathobase often seen as " mandible " and the genital operculum) . There is no See also:

• REASON (Lat. ratio, through French raison)

reason to suppose that any of the forms of limb observed in Arthropoda may not have been independently developed in two or more separate diverging lines of descent . Branchiae.—In connexion with the discussion of the limbs of Arthropods, a few words should be devoted to the gill-processes . It seems probable that there are branchial plumes or filaments in some Arthropoda (some Crustacea) which can be identified with the distinct branchial organs of Chaetopoda, which lie dorsal of the parapodia and are not part of the parapodium . On the other See also:

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

hand, we cannot refuse to admit that any of the processes of an Arthropod parapodium may become modified as branchial organs, and that, as a rule, branchial out-growths are easily developed, de now, in all the higher groups of animals . Therefore, it seems to be, with our present knowledge, a hopeless task to analyse the branchial organs of Arthropoda and to identify them genetically in groups . A brief See also:

• NOTICE

notice must suffice of the structure and history of the Eyes, the Tracheae and the so-called Malpighian tubes of Arthropoda, though special importance attaches to each in regard to the determination of the affinities of the various animals included in this great sub-phylum . The Eyes.—The Arthropod eye appears to be an organ of special character developed in the common ancestor of the Euarthropoda, and distinct from the Chaetopod eye, which is found only in the Onychophora where the true Arthropod eye is absent .

The essential difference between these two kinds of eye appears to be that the Chaetopod eye (in its higher developments) is a vesicle enclosing the lens, whereas the Arthropod eye is a See also:

• PIT (O. E. pytt, cognate with Du. put, Ger. Pfutze, &c., all ultimately adaptations of Lat. puteus, well, formed from root pu-, to cleanse, whence gurus, clean, pure)

pit or series of pits into which the heavy chitinous cuticle dips and enlarges knobwise as a lens . Two distinct forms of the Arthropod eye are observed—the monomeniscous (simple) and the polymeniscous (See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

compound) . The nerveend-cells, which lie below the lens, are part of the general epidermis . They show in the monomeniscous eye (see article ARACHNIDA, fig . 26) a tendency to group themselves into " retinulae," consisting of five to twelve cells united by See also:

• VERTICAL (from Lat. vertex, highest point)

vertical deposits of chitin (rhabdoms) . In the case of the polymeniscous eye (fig . 23, article ARACHNIDA) a single retinula or group of nerve-end-cells is grouped beneath each associated lens . A further complication occurs in each of these two classes of eye . The monomeniscous eye is rarely provided with a single layer of cells beneath its lens; when it is so, it is called monostichous (simple lateral eye of Scorpion, fig . 22, article ARACHNIDA) . More usually, by an infolding of the layer of cells in development, we get three layers under the lens; the front layer is the corneagen layer, and is separated by a membrane from the other two which, more or less, fuse and contain the nerve-end-cells (retinal layer) . These eyes are called diplostichous, and occur in Arachnida and Hexapoda (fig .

24, article ARACHNIDA) . On the other hand, the polymeniscous eye undergoes special elaboration on its lines . The retinulae become elongated as deep and very narrow pits (fig . 12 and explanation), and develop additional cells near the mouth of the narrow pit . Those nearest to the lens are the corneagen cells of this more elaborated eye, and those between the original retinula cells and the corneagen cells become firm and transparent . They are the crystalline cells or vitrella (see Watase, 7) . Each such complex of cells underlying the lenticle of a compound eye is called an " ommatidium "; the entire mass of cells underlying a monomeniscous eye is an " ommataeum." The ommataeum, as already stated, tends to segregate into retinulae which correspond potentially each to an ommatidium of the compound eye . The ommatidium is from the first segregate and consists of few cells . The compound eye of the See also:

• KING
• KING (O. Eng. cyning, abbreviated into cyng, cing; cf. O. H. G. chun- kuning, chun- kunig, M.H.G. kiinic, kiinec, kiinc, Mod. Ger. Konig, O. Norse konungr, kongr, Swed. konung, kung)
• KING [OF OCKHAM], PETER KING, 1ST BARON (1669-1734)
• KING, CHARLES WILLIAM (1818-1888)
• KING, CLARENCE (1842–1901)
• KING, EDWARD (1612–1637)
• KING, EDWARD (1829–1910)
• KING, HENRY (1591-1669)
• KING, RUFUS (1755–1827)
• KING, THOMAS (1730–1805)
• KING, WILLIAM (1650-1729)
• KING, WILLIAM (1663–1712)

king-crab (Limulus) is the only recognized instance of ommatidia in their simplest See also:

• STATE
• STATE, GREAT OFFICERS OF

state . Each can be readily compared with the single-layered lateral eye of the scorpion . In Crustacea and Hexapoda of all grades we find compound eyes with the more complicated ommatidia described above . We do not find them in any Arachnida .

It is difficult in the absence of more detailed knowledge as to the eyes of Chilopoda and Diplopoda to give full value to these facts in tracing the affinities of the various classes of Arthropods . But they seem to point to a community of origin of Hexapods and Crustacea in regard to the complicated ommatidia of the compound eye, and to a certain See also:

• ISOLATION

isolation of the Arachnida, which are, however, traceable, so far as the eyes are concerned, to a distant commonorigin with Crustacea and Hexapoda through the very simple compound eyes (monostichous, polymeniscous) of Limulus . The Tracheae.—In regard to tracheae the very natural tendency of zoologists has been until lately to consider them as having once developed and once only, and therefore to hold that a group " Tracheata " should be recognized, including all tracheate Arthropods . We are driven by the conclusions arrived at as to the derivation of the Arachnida from branchiate ancestors, independently of the other tracheate Arthropods, to formulate the conclusion that tracheae have been independently developed in the Arachnidan class . We are also, by the isolation of Peripatus and the impossibility of tracing to it all other tracheate Arthropoda, or of regarding it as a degenerate offset from some one of the tracheate classes, forced to the conclusion that the tracheae of the Onychophora have been independently acquired . Having accepted these two conclusions, we formulate the generalization that tracheae can be independently acquired by various branches of Arthropod descent in adaptation to a terrestrial as opposed to an aquatic mode of See also:

• LIFE

life . A great point of See also:

• INTEREST

interest therefore exists in the knowledge of the structure and embryology of tracheae in the different groups . It must be confessed that we have not such full knowledge on this head as could be wished for . Tracheae are essentially tubes like bloodvessels—apparently formed from the same See also:

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

tissue elements as bloodvessels—which contain See also:

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

air in place of blood, and usually communicate by definite orifices, the tracheal stigmata, with the See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere . They are lined internally by a cuticular See also:

• DEPOSIT (Lat. depositurn, from deponere, to lay down, to put in the care of)

deposit of chitin . In