Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/698

Rh 670 MOLLUSCA [CEPHALOPODA. Character. - Section b. Dccapoda CUondropliora. -Internal shell horny. Sub-section a. Myopsidse, (d Orb. ). Eye with closed cornea, so that the surrounding water does not touch the lens ; mostly frequenters of the coast. Family 1. Loligidse. Genera: Loligo, Schneid. (figs. 99, &c.); Loliolus, Steenstrup ; Scpioteuthis, Blv. ; [Tcuthopsis], Desl. ; Leptoteuthis], Meyer; [Bdcmiwscpia], Ag. ; [Bclotcuthis], Miinst. Family 2. Sepiolidse. Genera : Scpiola, Schneid. ; Rossia, Owen. Sub-section p. Oigopsidae (d Orb.). Eye with open cornea, so that the surrounding water bathes the anterior surface of the lens ; mostly pelagic animals. Family 3. Cranehiodse. Genus : Cranchia, Leach (fig. 94, C). Family 4. Loligopsidw. Genus : Loligopsis, Lam. (fig. 93, C). Family 5. Chciroteuthidse. Genera : Chciroteuihis, d Orb. (fig. 93, A) ; Histioteuthis, d Orb. Family 6. Thysanotcuthidse. Genus : Thysanotcuthis, Troschel (fig. 93, B). Family 7. 0?iychotcuthidse. Genera : Gonatus, Gray ; Onychoteuthis, Lichtenst. (fig. 97) ; Ony- chia, Lesueur ; Enoplotcuthis, d Orb. , Veranya, Krohn ; [Plesio- teiithis], A. Wag. ; [Celseno], Miinst. ; Dosidicus, Steenstrup ; Ommastrephes, d Orb. Sub-order 2. Octopoda. Clutractfrs. Dibranchiata with the fore-foot drawn out into eight arms only; suckers sessile, devoid of horny ring; eyes small, the FIG. 94. Octopodous Siphonopods ; one-fourth the natural size linear. A. Pinnoctopus cordiformis, Quoy and Gain (from New Zealand). B. Tremoc- topus violuceus, Ver. (from the Mediterranean). C. Cranchia scnbra, Owen (from the Atlantic Ocean ; one of the Decapoda). D. Cirrhoteuthis Miilleri Esch. (from the Greenland coast). outer skin can be closed over them by a sphincter-like movement. The body is short and rounded ; the mantle lias no cartilaginous locking apparatus, and is always fused to the head dorsally by a broad nuchal band. No buccal membrane surrounds the mouth. The siphon is devoid of valves. The oviducts are paired ; there are no nidamental glands. The viscero-pericardial space is reduced to two narrow canals, passing from the nephridia to the capsule of the genital gland. There is no shell on or in the visceral hump. Family l. Cirrhoteuthidse. Genus: Cirrhotcuthis, Esch. (Stiadcphorus, Reinh.) (fig. 94, D). Family l.Or.topodidse. Genera : Pinnodopus, d Orb. (fig. 94, A) ; Octopus, Lam. (fig. 95) ; Sc&urgu?, Troscli. ; Eledone, Leach ; Bolitsena, Steenstrup. Family 3. Philoncxidse,. Genera: Tremoctopus, Delle Chiaje (Philoncxis, d Orb.) (fig. 94, B) ; Parasira, Steenstrup (Octopus catenulatus, Fer., is the female, and Octopus carcna, Ver., is the male of the one species of this genus according to Steenstrup (fig. 96) ) ; Argonauta, L. (the shell of this genus is formed only in the female by the expanded ends of the two large &quot;arms &quot; of the fore-foot). Fio. 05. A. Male specimen of Octopus grocnlandicus, with the third arm of the right side hectocotylized. B. The extremity of the hectocotylized arm magnified. Further Remarks on the Cephalopoda. In order to give a more precise conception of the organization of the Cephalo poda in a concrete form we select the Pearly Nautilus for further description, and in pass ing its structure in review we shall take the opportunity of comparing here and there the peculiarities presented by that animal with those obtaining in allied forms. In the last edition of this work the Pearly Nautilus was made the subject of a de tailed exposition by Professor Owen, and it has seemed accord ingly appropriate that it should be somewhat fully treated on the present occasion also. The figures which illustrate the pre sent description are (excepting fig. 89) original, and prepared from dissections (made under the direction of the writer) of a male and female Nautilus pompilius, lately purchased for the Museum of University College, London. Visceral Hump and Shell. The visceral hump of Nautilus (if we exclude from considera tion the fine siphuncular pedicle FIO. oc. Male of Powira eaten which it trails, as it were, behind it) is very little, if at all, affected by the coiled form of the shell which it carries, since the animal always slips forward in the shell as it grows, and inhabits a cham ber which is practically cylindri cal (fig. 89). Were the deserted chambers thrown off instead of being accumulated behind the inhabited chamber as a coiled series of air-chambers, we should have a more correct indication in the shell of the extent and form of the animal s lata, Steenstrup (Octopus carena, Ver.), showing the hectocotylized arm. fl, f2, (3, t*, the first, second, third, and fourth arms or pro cesses of the fore-foot ; fc, the third arm of the right side hecto cotylized ; x, the apical sac of the hectocotylized arm ; y, the fila ment which issues from the sac when development is complete ; i, the siphon. (From Gegeubaur.)