Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V05, Page 698 of the 1911 Encyclopedia Britannica.
Spread the word: it!
U1L t~ A, Cheiroteuthis Veranyi, d'Orb. (from the Mediterranean). B, Thysanoteuthis rhombus, Troschel (from Messina). C, Loligopsis cyclura, Fer. and d'Orb. (from the Atlantic Ocean). nized. One or two pairs of large salivary glands with long ducts are present. An ink-sac formed as a diverticulum of the rectum and opening near the anus is present in all Dibranchiata (fig. and has been detected even in the fossil Belemnitidae. Branchial hearts are developed on the two branchial afferent blood-vessels (fig. 28, vc', vi). In the Dibranchiata the shell shows various stages of degeneration, culminating in its complete disappearance in Octopus. As in other Mollusca, there is a tendency in Cephalopods for the mantle to extend over the outside of the shell from its edges, and when these secondary mantle-folds entirely cover the shell and meet or fuse together the shell is surrounded by the mantle both externally and internally, and is said to be internal, though it remains always a cuticular structure ex- ternal to the epidermis. This process is generally accompanied by a reduction of the size of the shell in comparison with that of the body, so that the relations of the two are gradually reversed, the body outgrows its house and instead of the 25, t), A, Conoteuthis dupiniana, d'Orb. (from the Neocomian of France). Shell Sepia orbigniana. Fer. (Mediterranean). Shell of Spirulirostra Bellardii, d'Orb. (from the Miocene of Turin). The specimen is cut so as to show in section the chambered shell and the laminated " guard " deposited upon its surface. D, Shell of Spirula laevis, Gray (New Zealand). B, C, mantle being enclosed by the shell, the shell is enclosed by (fig. 21) and Sepiolidae. Lastly, in the Octopoda the shell is the mantle. The earliest stage of this process is shown in represented only by small chitinous rudiments to which the the recent Spirula, retractor muscles of the head and funnel are attached; these are though it is perhaps paired in Octopus, unpaired in other cases as in Cirrhoteuthis. not impossible that in some of the later fossil Ammonoids the shell was becoming more and more internal. The shell of Spirula (fig. 18) is coiled somewhat like that of Nautilus, but the coils are not in contact, the direction of the coil is endogastric or ventral instead of exogastric, and the shell is very much smaller than the body. Like that of Nautilus it is divided by septa and traversed by a siphuncle. The relation of the animal to the terminal chamber is as in Nau-, tilus, but the body extends far beyond the aperture, and folds of the mantle grow up over the shell and cover it everywhere except part of the dorsal and ventral surfaces. The next modification in the en- closed shell is the addition to it of secondary deposits of calcareous matter, by the inner surface of the shell-sac. Successive layers are de- posited on the posterior part of the original shell, whether coiled or straight, and these layers form a conical mass, which may attain great thickness. A somewhat coiled shell with such a deposit is seen in Spirulirostra (fig. 17, C) of the Miocene. In the next P stage of modification secondary secre- tion forms a long and broad projection of the dorsal lip of the aperture; this is well developed in the belemnites (fig. 19). Thus in these modi- fied shells three parts are to be distinguished: the original septate shell, which has been called the phragmacone; the posterior conical deposit, called the rostrum or guard; and the anterior somewhat flat projec- tion, called the proostracum. In the living Dibranchiata other than Spirula the phrag- macone and rostrum have be- come very rudimentary. The FIG. Pp.—Diagram of shell of Sepia (fig. 20) consists Belem nite (after Phillips). almost entirely of the proosr. Horny pen or Pro- ostracum " ; a, conical tracurn, the little ventral cavity or " alveolus," in hollow posteriorly representing which the chambered the phragmacone, and the pos- phragmacone " (p) is tenor pointed projection, the contained; g, " guard," or " rostrum." rostrum. In the Oigopsida the shell is represented by a pro- ostracum which is no longer calcified but forms a chitinous In Argonauta (the paper nautilus) the female only possesses plume or gladius, and a similar rudiment occurs in Loliginidae a shell, in which the body is contained; but this is not p..e After Chun, from Lankester's Treatise on Zoology. A, Dorsal aspect. pa, Mantle. B, Ventral aspect. po, Posterior fossa. a, Arms. sh, Shell. e, Eyes. te, Tentacular arms. fi, Fins. td, Terminal pallial fu, Funnel. disk. The early appearance of the sac of the mantle in which the shell is enclosed has led to an erroneous identification of this sac with the primitive shell-sac or shell-gland of the Molluscan embryo. The first appearance of the shell-sac in Dibranchiata is shown in figs. 35, 36. Its formation as an open upgrowth of the centro-dorsal area, and the fact that it appears and disappears without closing in Argonauta and Octopus, was demonstrated by E. Ray Lankester. homologous with the true shell in other cases; it is a structure sui generis secreted by the expanded arms of the dorsal pair which are closely applied to it on either side (fig. 22). Head, Foot, Mantle and Mantle-cavity.—If we now compare the fore-foot of the Dibranchiata with that of Nautilus, we find in the first place a more simple arrangement of its lobes, which are either four or five pairs of tapering processes (called " arms "), arranged in a series around the buccal cone, and a sub- stitution of suckers for tentacles on the surface of these lobes (figs. 15 and 24). The most dorsally placed pair of arms, corresponding to the two sides of the hood of Nautilus, are in reality the most anterior, and are termed the first pair. In the Octopoda there are four pairs of these arms (fig. 38), in the Decapoda five pairs, of which the fourth is greatly elon- gated (figs. 15, i6). In Sepia, Sepiola and Rossia, each of these long arms is withdrawn into a pouch beside the head, and is only ejected for the purpose of prehension. In Loligo they are completely retractile, very slightly FIG. 23.—Head and circum- arm. (From Gegenbaur.) oral processes of the fore-foot tI t2 t', t', The first, second, of Onychoteuthis (from Owen). third and fourth arms a, Neck. b, Eye. or processes of the fore- c, The eight short arms. foot. d, Long prehensile arms, the h, The third arm of the clavate extremities of right side hectocoty- which are provided with lized. suckers at e, and with a x, The apical sac of the double row of hooks be- hectocotylized arm. yond at f. The temporary y, The filament which conjunctjpn of the arms issues from the sac by means of the suckers when development is enables them to act in complete. combination. i, The siphon. so in the majority of the Oigopsida, and in Rhynchoteuthis they are united to form a beak-like appendage. A gradual reduction of the tentacular arms can be seen in the Decapoda, leading to their total absence in Octopoda; thus in Leachia, Chaunoteuthis and others these arms are reduced to mere stumps. In some Cheiroteuthidae and Cranchiidae the ordinary or sessile arms, especially the dorsal pairs, are reduced. In the Octopoda they are not unfrequently connected by a web, and form an efficient swimming-bell, e.g. iu Cirrhoteuthidae and Amphiiretidae. The suckers are placed on the adoral surface of the arms, and may be in one, two or four rows, and very numerous. In place of suckers in some genera, e.g. Veranya, we find on certain arms or parts of the arms horny hooks; in other cases a hook rises from the centre of each sucker. The hooks on the long arms of Onychoteuthis are drawn in fig. 23. In various species of Cheiroteuthis the suckers on the tentacular arms are very feeble, but the bottom of the cup is covered by a number of anastomosed epithelial filaments which are used as a fishing-net. The fore-foot, with its apparatus of suckers and hooks, is in the Dibranchiata essentially a prehensile apparatus, though the whole series of arms in the Octopoda serve as swimming organs, and in many (e.g. the common octopus or poulp) the sucker-bearing surface is used as a crawling organ. In the males of theF Dibranchiata one of the arms is more or less lP vp . r+ G a!i~ I~!I1iy --C C, The head. apparatus " characteristic J, The mid-foot or siphon, of Decapoda, not found in which has been cut open Octopoda. so as to display the valve i. g, The azygos genital papilla R, The glandular tissue of the and aperture. left nephridium or renal- 'i, Valve of the siphon (possibly sac, which has been cut the rudimentary hind-foot). open (see fig. 29). In, Muscular band connected P, P, The lateral fins of the with the fore-foot and mantle-skirt. mid-foot (siphon) and Br, The single pair of branchiae identical with the muscular (ctenidia). mass k in fig. 3. a, The anus—immediately r, Renal papillae, carrying the below it is the opening of apertures of the nephridia. the ink-bag., Branchial efferent blood- c, Cartilaginous socket in the vessel siphon to receive c', the', Bulbous enlargements of cartilaginous knob of the the branchial blood-vessels mantle-skirt—the two con- (see figs. 28, 29). stituting the " pallial hinge t, Ink-bag. modified in connexion with tit reproductive function, and is called the " hectocotylized arm." This name is derived from the condition assumed by the arm in those cases in which its modification is carried out to the greatest extent. These cases are those of the Octopods Argonauts argo .and Ocythoe catenulata (fig. 24). In the males of these the third arm (on the left side in Argonauta, on the right side in Ocythoe) is found before the breeding season to be represented by a globular sac of integument. This sac bursts, and from it issues an arm larger than its neighbours, having a small sac at its extremity in Ocythoe (fig. 24. X), from which subsequently a long filament issues. Before copulation the male charges this arm with the spermatophores or packets of spermatozoa removed from its generative orifice beneath the mantle-skirt, and during coitus the arm becomes detached and is left adhering to the female by means of its suckers. A new arm is formed at the cicatrix before the next breeding season. The female, being much larger than the male, swims away with the detached arm lodged beneath her mantle-skirt. There, in a way which is not understood, the fertilization of the eggs an ~.. \re n-n-a vise. er. ° i t 9 apet. , o, The fifth or lowermost lobe of the fore-foot. [foot. p,' The third lobe of the fore- q, The buccal membrane. v, The upper beak or jaw. s, The lower beak or law. t, The lingual ribbon. x, The viscero-pericardial sac. n.c, The nerve-collar. cr, The crop. glee, The gizzard. an, The anus. c.t, The left ctenidium or gill-plume. vent, Ventricle of the heart. a.b.v, Afferent branchial vessel. e.b.v, Efferent branchial vessel. re, Renal glandular mass. n.n.a, Left nephridial aperture. visc.per.apert, Viscero-pericardial aperture (see fig. 29). br.b, Branchial heart. app, Appendage of the same. i.s, Ink-bag. dorsally along the whole of their afferent borders. On each side of the branchia is a series of lamellae, least in number in the Octopoda. Each lamella is transversely folded, and the folds are in turn folded, so that the respiratory surface is increased. On the somatic wall of the pallial cavity, between and ventral to the gills, are the following apertures: the anus and opening of the ink-sac, close together in the median line; a pair of apertures of the renal sacs, on either side of the median line; external to the renal orifice, on the left side, the genital aperture in Cirrhoteuthidae and Myopsida. In other Octopoda, and in nearly all the Oigopsida among the Decapoda, the genital ducts are paired in the female, but only the left is developed in the male. The funnel forms a complete tube in the Dibranchiata, and in the majority of the Decapoda, as in Nautilus, it is provided with an internal valve projecting from its somatic surface, which allows water to pass outwards but prevents it passing inwards. The mantle performs rhythmical respiratory movements of expansion and contraction, the water entering between funnel and mantle and passing out through the funnel. In Decapoda the edge of the mantle bears internally on each side a cartilaginous projection which fits into a corresponding depression on the external surface of the funnel; this is called the " resisting apparatus," and serves to make the union of mantle and funnel firmer during expiration. More powerful expiratory movements are used for sudden retrograde locomotion through the water- 697 Luminous Organs.—In certain Oigopsida living in deep water, e.g. Histioteuthis, Calliteuthis, Histiopsis, Pterygioteuthis, the surface of the skin bears photogenous organs directed towards the oral extremity. Anatomically these consist of a deeper photogenous layer and a more superficial refracting layer. In some cases, e.g. Pterygioteuthis, they occur even within the mantle-cavity. Fins.—In the majority of the Decapoda and in the Cirrhoteuthidae, the mantle is produced into lateral symmetrical expansions which have the function of fins. They originate at the aboral extremity where they remain in Spirula (fig. i8). In most other Oigopsida they are terminal, but more dorsal than ventral, e.g. Loligopsis (fig. i6), and there may be two on each side, as in Grimalditeuthis. In other cases they extend laterally along a greater length of the body, as in Sepia (fig. i5). In Ctenopteryx they have a superficial resemblance to the fins of fishes, consisting of a thin membrane supported by a series of muscular rods. Chromatophores.—These are characteristic of the Dibranchiata, apparently absent in Nautilus. They are originally single cells of ectodermic origin which sink below the epidermis and become connected with radiating muscular fibres. The cells are single but multinuclear. Different cells contain pigments of different colours, yellow. brown, red or blue. Each cell in life is in constant tremulous movement; under the influence of nervous excitement the cells are suddenly expanded or contracted, producing blushes of colour and pallor. By reflex action of which the afferent stimulus acts upon the eyes as in fishes, the chromatophores assume a condition which approximates the colour of the animal to that of surrounding objects. In the Decapoda there are also reflecting elements which produce iridescent hues. Aquiferous Cavities.—In addition to the pockets into which the tentacular arms of Decapoda are retracted, there are in several Dibranchiata cavities in the integument which open to the exterior by special pores but have no communication with the vascular system or other internal cavities of the body. In Ocythoe there are such pores on the back of the head and at the base of the funnel; buccal pouches on the ventral side of the mouth, internal to the arms, occur in some genera, one in Loligo, two in Sepia. In some species of Sepia there are pouches in the mantle. Alimentary Tube.—The principal differences from Nautilus are the following: the mandibles are similar in shape, but are chitinous, not calcified. In the radula there are three teeth on each side of the median tooth in each row, except in Gonatus, in which there are only two lateral teeth, and the Cirrhoteuthidae, in which the radula has entirely disappeared. In front of the radula is the so-called tongue, a fleshy projection corresponding to the sub-radular organ of other Mollusca. In most of the Dibranchiata there are two pairs of salivary glands. In the Decapoda the ducts of the posterior pair unite into a c, median duct which opens on the surface of the sub-radular organ. The anterior pair is but slightly developed except in the Oigopsida. In the Octopoda there are also two pairs, but the posterior pair, except in Cirrhoteuthis where they are absent, are large and displaced backwards, being situated near the oesophageal proventriculus. Connected with the intestine immediately beyond the pylorus is a thin-walled caecum, spherical in Rossia and Leachia, elongated in Loligo, but usually coiled into a spiral (fig. 27). The hepatic ducts open into the caecum. The liver is developed as a paired gland, more or less fused into one in the adult, but the ducts are always paired. The ducts are covered by a number of glandular follicles forming what is called the pancreas. The ink-sac, absent in Nautilus, is a rectal caecum developed from its dorsal wall. It is present in all Dibranchiata except Octopus arcticus, 0, piscatorum and Cirrhoteuthis. It consists of a deeper part or gland proper and a reservoir. It extends to the posterior extremity of the body in Sepia, but in Octopoda is usually embedded in the surface of the liver. The pigment of the secretion is melanin, and its function is to produce a dense opacity in the water, which conceals the animal. Vascular System (fig. 28).—The ventricle lies in the pericardial cavity, except in Octopoda where this cavity is much reduced. The auricles, one pair, are contractile expansions of the efferent branchial vessels. The heart gives off an anterior or cephalic and a posterior or abdominal aorta. The vascular system is almost perfect, arteries and veins being united by capillaries. The principal vein is a-vena is effected. Specimens of the female Ocythoe with the detached arm adherent were examined by Cuvier, who mistook the arm for a parasitic worm and gave to it the name Hectocotylus. Accordingly, the correspondingly modified arrns of other Cephalopoda are said to be hectocotylized. J. J. S. Steenstrup has determined the hectocotylized condition of one or other of the arms in a number of male Dibranchs as follows: in all, excepting Argonauta and Ocythoe and Tremoctopus, the modification of the arm is slight, consisting in a small enlargement of part or the whole of the arm, and the obliteration of some of its suckers; in Octopus and Eledone the third right arm is hectocotylized; in Rossia and Sepiola the fourth left arm is hectocotylized along its whole length, and the fourth right arm also in the middle only; in Sepia the fourth left arm is modified at its base only; in Sepioteuthis, the same at its apex; in Loligo, the same also at its apex; in Loliolus, the same along its whole length; in Ommatostrephes, Onychoteuthis and Loligopsis no hectocotylized arm has hitherto been observed. Thus, speaking generally, it is one or both of the fourth pair of short arms which are modified in the Decapoda, of the third pair in the Octopoda. In the pallial cavity are situated one pair of gills in the Dibranchiata ,(fig. 25), attached c. t. a.b v v d b n r a .r r e.b.v a, Shell (here enclosed by a growth of the mantle). b, The nuchal plate (here a cartilage). c, (The reference line should be continued through the black area representing the shell to the outline below it), the integument covering the visceral hump. d, The reflected portion of the mantle-skirt forming the sac which encloses the shell. e, The inferior margin of the mantle-skirt (mouth of the pallial chamber). The pallial chamber. The vertically cut median portion of the siphon. The valve of the siphon! The two upper lobes of the fore-foot. [the same. n, The long prehensile arms of f, g, i, m, Fig. 27. — Alimentary canal of Loligo sagittata (from Gegenbaur). The buccal mass is omitted. oe, Oesophagus. v, The stomach opened longitudinally. x, Probe passed through the pylorus. Commencement of the caecum. Its spiral portion. Intestine. Ink-bag. Its opening into the rectum. i, a, b, cava passing backwards ventrally from the cephalic region and dividing into two afferent branchial veins, each of which receives a c, Ventricle of the heart. a, Anterior artery (aorta). a', Posterior artery. v, The right and left auricles (enlargements of the efferent branchial veins). v', Efferent branchial vein on the free face of the gill-plume. v.c, Vena cava. pallial and an abdominal vein. Each of these afferent branchial vessels is enclosed in the cavity of a renal organ and is covered externally by the glandular tissue which forms the excretory part of the " kidney " (fig. 29). Each afferent vessel is expanded into a np re v.c, Vena cava. [of the same. np, r.d.v.c, Right descending branch r.d.v.c, Left descending branch of the same. v.b.a, Vein from the ink-bag. v.m, Mesenteric vein. v.g, Genital vein. v.a.d, Right abdominal vein. v.a.s, Left abdominal vein. v.p.d, Right pallial vein. v.p.s, Left pallial vein. c.b, Branchial heart. x, Appendage of the same. a.r, c.v, Capsule of the branchial w.k, heart. contractile branchial heart, which is provided with a glandular appendage. The latter corresponds to the glandular masses which are attached to the afferent branchial veins in Nautilus, and to the pericardial glands of other Molluscs. Coelom.—The coelom forms a large sac with a constriction between ccr
End of Article: U1L

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click and select "copy." Paste it into a website, email, or other HTML document.