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U1L t~ A, Cheiroteuthis Veranyi, d'See also:Orb. (from the Mediterranean). B, Thysanoteuthis rhombus, Troschel (from See also:Messina). C, Loligopsis cyclura, Fer. and d'Orb. (from the See also:Atlantic Ocean). nized. One or two pairs of large salivary glands with See also:long ducts are See also:present. An See also:ink-See also: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 See also:hearts are See also:developed on the two branchial afferent See also:blood-vessels (fig. 28, vc', vi). In the Dibranchiata the See also:shell shows various stages of degeneration, culminating in its See also:complete disappearance in See also:Octopus. As in other See also:Mollusca, there is a tendency in Cephalopods for the See also:mantle to extend over the outside of the shell from its edges, and when these secondary mantle-folds entirely See also:cover the shell and meet or fuse together the shell is surrounded by the mantle both externally and internally, and is said to be See also:internal, though it remains always a cuticular structure ex- ternal to the epidermis. This See also:process is generally accompanied by a reduction of the See also:size of the shell in comparison with that of the See also:body, so that the relations of the two are gradually reversed, the body outgrows its See also:house and instead of the
25, t),
A, Conoteuthis dupiniana, d'Orb. (from the Neocomian of See also:France).
Shell See also:Sepia orbigniana. Fer. (Mediterranean).
Shell of Spirulirostra Bellardii, d'Orb. (from the See also:Miocene of See also:Turin). The specimen is cut so as to show in See also:section the chambered shell and the laminated " guard " deposited upon its See also:surface.
D, Shell of Spirula laevis, See also: The earliest See also:stage of this process is shown in represented only by small chitinous rudiments to which the the See also:recent Spirula, retractor muscles of the See also:head and See also: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 See also: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 See also:animal to the terminal chamber is as in Nau-, tilus, but the body extends far beyond the See also:aperture, and folds of the mantle grow up over the shell and cover it everywhere except See also: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 See also:matter, by the inner surface of the shell-sac. Successive layers are de- posited on the posterior part of the See also:original shell, whether coiled or straight, and these layers See also:form a conical See also:mass, which may attain See also:great thickness. A somewhat coiled shell with such a See also: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 See also:projection of the dorsal See also: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 See also: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.—See also:Diagram of shell of Sepia (fig. 20) consists Belem nite (after See also:Phillips). almost entirely of the proosr. Horny See also:pen or See also: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 See also: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 See also:paper nautilus) the See also: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 See also:Treatise on See also: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 See also:early See also:appearance of the sac of the mantle in which the shell is enclosed has led to an erroneous See also:identification of this sac with the See also:primitive shell-sac or shell-gland of the Molluscan embryo. The first appearance of the shell-sac in Dibranchiata is shown in See also:figs. 35, 36. Its formation as an open upgrowth of the centro-dorsal See also:area, and the fact that it appears and disappears without closing in Argonauta and Octopus, was demonstrated by E. See also:Ray Lankester. homologous with the true shell in other cases; it is a structure sui generis secreted by the See also:expanded arms of the dorsal pair which are closely applied to it on either See also:side (fig. 22). Head, See also:Foot, Mantle and Mantle-cavity.—If we now compare the fore-foot of the Dibranchiata with that of Nautilus, we find in the first See also:place a more See also:simple arrangement of its lobes, which are either four or five pairs of tapering processes (called " arms "), arranged in a See also:series around the buccal See also: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 See also: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 See also: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- See also:arm. (From See also:Gegenbaur.) oral processes of the fore-foot tI t2 t', t', The first, second, of Onychoteuthis (from See also:Owen). third and fourth arms a, See also:Neck. b, See also:Eye. or processes of the fore- c, The eight See also: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 See also:double See also: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 See also:act in complete. See also:combination. i, The See also:siphon. so in the See also:majority of the Oigopsida, and in Rhynchoteuthis they are See also:united to form a See also:beak-like appendage. A See also:gradual reduction of the tentacular arms can be seen in the Decapoda, leading to their See also:total See also:absence in Octopoda; thus in Leachia, Chaunoteuthis and others these arms are reduced to See also:mere stumps. In some Cheiroteuthidae and Cranchiidae the See also:ordinary or sessile arms, especially the dorsal pairs, are reduced. In the Octopoda they are not unfrequently connected by a See also:web, and form an efficient See also:swimming-See also: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 See also:hook rises from the centre of each sucker. The hooks on the long arms of Onychoteuthis are See also:drawn in fig. 23. In various See also:species of Cheiroteuthis the suckers on the tentacular arms are very feeble, but the bottom of the See also:cup is covered by a number of anastomosed See also:epithelial filaments which are used as a fishing-See also: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 See also:organs, and in many (e.g. the See also:common octopus or poulp) the sucker-bearing surface is used as a crawling See also:organ. In the See also: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 See also:mid-foot or siphon, of Decapoda, not found in which has been cut open Octopoda. so as to display the See also:valve i. g, The azygos genital papilla R, The glandular See also:tissue of the and aperture. See also:left nephridium or renal- 'i, Valve of the siphon (possibly sac, which has been cut the rudimentary See also:hind-foot). open (see fig. 29). In, See also:Muscular See also: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. v.br, Branchial efferent blood- c, Cartilaginous socket in the See also:vessel siphon to receive c', the v.br', Bulbous enlargements of cartilaginous knob of the the branchial blood-vessels mantle-skirt—the two See also:con- (see figs. 28, 29). stituting the " pallial See also:hinge t, Ink-bag. modified in connexion with tit reproductive See also:function, and is called the " hectocotylized arm." This name is derived from the See also: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 See also: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 See also: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 See also:lobe of the fore-foot. [foot. p,' The third lobe of the fore- q, The buccal membrane. v, The upper beak or See also:jaw. s, The See also:lower beak or See also:law. t, The lingual ribbon. x, The viscero-pericardial sac. n.c, The See also:nerve-See also:collar. cr, The See also:crop. See also:glee, The gizzard. an, The anus. c.t, The left ctenidium or gill-plume. vent, Ventricle of the See also: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 See also: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 See also:respiratory surface is increased. On the somatic See also:wall of the pallial cavity, between and ventral to the gills, are the following apertures: the anus and opening of the ink-sac, See also:close together in the median See also:line; a pair of apertures of the renal sacs, on either side of the median line; See also: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 See also: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 See also: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 See also:union of mantle and funnel firmer during expiration. More powerful expiratory movements are used for sudden See also: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 See also:fibres. The cells are single but multinuclear. Different cells contain See also:pigments of different See also:colours, yellow. See also: 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 See also:special pores but have no communication with the vascular See also:system or other internal cavities of the body. In Ocythoe there are such pores on the back of the head and at the See also: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 See also:principal See also:differences from Nautilus are the following: the mandibles are similar in shape, but are chitinous, not calcified. In the radula there are three See also: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 See also: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 See also:intestine immediately beyond the pylorus is a thin-walled caecum, spherical in Rossia and Leachia, elongated in Loligo, but usually coiled into a See also:spiral (fig. 27). The hepatic ducts open into the caecum. The See also: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 See also: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 See also: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, See also:arteries and See also: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 See also:Cuvier, who mistook the arm for a parasitic See also:worm and gave to it the name Hectocotylus. Accordingly, the correspondingly modified arrns of other See also: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 See also:middle only; in Sepia the fourth left arm is modified at its base only; in Sepioteuthis, the same at its See also: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 See also:plate (here a See also:cartilage). c, (The reference line should be continued through the See also: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 See also:canal of Loligo sagittata (from Gegenbaur). The buccal mass is omitted. oe, See also:Oesophagus. v, The See also: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 See also:free See also: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 " See also: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 See also: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, See also: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. Additional information and CommentsThere are no comments yet for this article.
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