Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/775

Rh CUTTLE F I S H 739 Cephalopod in which an external shell is present is the Paper Nautilus (Argonauta). The shell, moreover, is only possessed by the female Argonaut the male being shell: less and it is in no way comparable as regards its mode of origin and its morphological sig nificance with the shell of the ordi nary testaceous Mollusks in gene ral, or of the Tetra- Lranchiate Cepha lopoda in particu lar. The shell of the Argonaut is in volute, one-cham bered, and calcare ous, of most grace ful outlines and ornamentation. It is not secreted by the mantle, nor is the animal attach ed to it by any organic connection hence the long controversy as to vhprViprtlip Arrra * IG - 5 - Argonauta argo, the &quot;Taper Nautilus, Uetner the ArgO- female _ The animal is represented In its shell, naut truly owned but the webbed dorsal arms are separated from the the shell it inha- 8he11 which they ordlnaril &amp;gt;- cmbrace - bited, or had not rather simply obtained it by plunder, as the Hermit-Crab seizes any empty shell which may be suitable for its temporary habitation. It is, however, now known that the shell of the Argonaut is secreted by the two dorsal arms of the female, which are expanded or webbed, and closely embrace the shell which they produce. These two arms, in their natural position, are bent backwards, so as to allow the animal to inhabit the shell. The animal sits in the shell, with its funnel turned towards the keel, and the apex of the shell is empty, and is used simply as a receptacle for the clustered eggs. The processes of reproduction and development in the cuttle-fishes are of great interest. The males and females are generally more or less unlike externally this difference being most marked in the Argonaut, in which the male is very much smaller than the female, and in addition possesses no shell. The reproductive organs of the female consist of a single ovary, situated at the hinder end of the body, and inclosed in a pouch of the peritoneum, from which one or two oviducts are continued to open into the mantle-cavity, generally near the base of the funnel. The eggs are discharged into the peri toneal sac surrounding the ovary, and are then taken up by the ovi ducts and conveyed into the mantle-cavity. When finally extruded, the impregnated eggs are found to be inclosed, singly or many together, in special capsules, which are usually attached in bunches to some foreign body. These egg-capsules are produced by the so-called &quot; nidamental glands,&quot; which in some genera (e.g., Sepia and Loligo) are of large size, and are appended to the proper gene rative organs. The reproductive organs of the male cuttle-fishes consist of a testis placed at the hinder extremity, like the ovary of the female, and- inclosed in a peritoneal sac. The spermatozpids are discharged into this sac by the rupture of the secreting tubes, and are conveyed to the exterior by a tubular &quot; vas deferens,&quot; which is dilated in its course into a &quot; vesicula seminalis,&quot; and ulti mately opens into the mantle-cavity by a papilliform &quot;penis&quot; situated close to the anus. Before the vas deferens finally termin ates in this way, it is usually expanded into a special dilatation (&quot; bursa sperm atophorum &quot;), in which are packed away the so-called &quot;spermatophores,&quot; or &quot;moving filaments of Needham.&quot; These singular bodies are whitish filaments, 6 or 8 lines in length, composed of aggregations of spermatozoids inclosed in a covering originally of an albuminous nature, but ultimately becoming deve loped into two membranes which have a complicated arrangement. When set free and moistened, the spermatophores exhibit active ver micular movements, and under suitable circumstances rupture and discharge their contained spermatozoa. The reproductive act in the cuttle-fishes is only. imperfectly known; but true intromission is certainly impossible. According to the observations of Aristotle, the poulpes and calamaries perform this act by clinging to each other, mouth to mouth, with the suckers of the arms in mutual apposition, the former seeking the bottom, whilst the latter move frdely in the water. It is known now, in this connection, that one of the arms of the male cuttle-fishes is pecu liarly modified, the arm thus affected beinor said to be &quot;hecto cotylized.&quot; In some forms, this hcctocotyli^cd arm differing in its position in different cases is not so conspicuously altered as to attract immediate attention, and it does not appear clear that it plays necessarily any part in the reproductive act, though the alteration of form is undoubtedly primarily sexual. In certain forms, however (viz. Argonauta argo, Trcmodopus violaccus, T. Quoyanus, and Octopus carena) the hectocotylized arm is the efficient agent in the act of reproduction. It is longer and thicker than the other arms, prolonged at its extremity into along filament, and possessing posteriorly a sac which is filled with spermatophores. During the act of reproduction, the hectocotylized arm is detached by the male, and is deposited, with its freight of spermatophores, within the mantle-cavity of the female. The terminal filament is perforated by a tube, by which the spermatophores are conveyed to the ova, and impregnation is thus effected. When thus detached, the hectocotylized arm is capable of independent movement, and when first found in this free condition within the mantle-sac of the female Argonaut it was regarded as a parasitic worm. Under this belief Delle Chiaje described it as the Trichocephalus acctabularis, and Cuvier called it (in the Octopus) the Hcdocotylus Octopodis. Both these names are in allusion to the suckers which the arm carries, and the name of &quot; hectocotylus &quot; is still applied to the detached arm, whereas the arm, if not detached, is simply said to be &quot; hectocotylized.&quot; As before remarked, it is not absolutely certain that the hectocotylized arm is invariably employed as a repro ductive agent; and certainly it is only occasionally detached. According to Steenstrup, however, the hectocotylized arm, when not detached, is employed by the male to transfer the spermato phores to the female during the act of reproduction, the spermatic filaments being either placed withiu the mantle-cavity, or fixed to FIG. 6. a.Malo of Argonauta aryo,vfifh thehoctocotylizcd arm Still contained in its enveloping cyst, four times enlarged (after H. MUIler). b, Hectocotylus of Tremoctopus i iolaceus (after Kb lliker). the internal surface of the buccal cavity of the females. How tlw spermatophores are transferred from the seminal ducts of the male to the sac contained in the interior of the hectocotylized arm is still uncertain; but Leuckart has shown that the sac in question does actually communicate with the surface by a distinct aperture. The development of the cuttle-fishes can be barely touched upon here. After fertilization the ovum undergoes a partial segmentation, as in birds and reptiles, and there is formed at one pole a germinal disc (&quot;blastoderm&quot;), which is at first divided into two parts by a primitive furrow, then into four by a secondary furrow intersecting the first at right angles, and then into eight. An inner germinal layer is then formed (according to the researches of Kay Lankester on Loligo) quite independently of the outer one; and the two layers then grow over the entire yolk and completely inclose it. The un- segmented portion of the yolk is gradually absorbed by the grow ing embryo, but obtains no direct connection with the alimentary tube, the latter originating from the primitive invagination of the outer layer of the blastoderm, instead of being formed, as in verte brates, by its inner layer. As regards their distribution in space, the cuttle-fishes are all marine, active, rapacious, and carnivorous in their habits, swim ming vigorously by means of the jets of water emitted from tho funnel, or in an opposite direction by means of fins, and creep- ino- about the sea-bottom by means of the prehensile arms.