274 



THE CEPHALOPODA. 



00" 



J.0O. 



Spirida,'^ an analogous calcareous tube extends close upon the inner sur- 

 face of the shell from one septum to another. The animal, whose trunk 

 occupies only the first chamber, is loosely attached to it by the cartilaginous 

 border of its mantle. 



With Nautilus, this border has a lobe which extends along the back of 

 the animal, sur-ounding the spiral portion of the shell.*'" With all the 

 Nautilina, there is another prolongation in the form of a membranous 

 tube, or Slpho, which arises from the posterior part of the body, — trav- 

 erses the orifices or calcareous tubes of the septa, and penetrates even into 

 the last chambers of the shell. These chambers are lined with a thin mem- 

 brane, and have no external communication except through the Siphon. 



2. With the Loligina, an internal shell lies free in the dorsal portion of 

 the mantle. In most genera, it is composed of a homogeneous, horny 

 substance, of a yellowish-brown color, and has a form like a feather 

 {Calamus), or the head of a lance. At one of its extremities is an attenu- 

 ated stem, and two delicate lateral winglets of variable length.*'^' With 

 Sepia, this shell differs very much from that of the other Loligina. Its 

 two surfaces are covered by very distinct calcareous layers, which have 

 erroneously given it the name of Os sepiae.^^^ As a whole, it is tongue- 

 shaped ; its two surfaces are convex and its borders are sharp. Behind, 

 the lateral borders become thinner and are slightly bent toward the ventral 

 surfiice ; and a short conical point projects from the middle of the pos- 

 terior border. The horny substance is reduced to a thin sheet, situated 

 between the calcareous layers, but its borders usually extend out beyond 

 those of these last. The calcareous layer of the dorsal surface is very 

 thin, but quite solid, and its surface in front, is granulated and striated ; 

 that of the ventral surface, on the other hand, is very thick, especially 

 in the middle, and its very loose tissue contains numerous quite thin, 

 porous lamellae, which, superposed almost horizontally, alternate regularly 

 with layers of small, trausversejy-striated, dichotomous, vertical prisms.*'' 

 This ventral layer is truncated obliquely from its middle backwards, and 

 the horizontal layers may easily be counted upon its truncated surface.'** 



S De Blfinville, Ibid. p. 18, PI. I. fig. 6, A-F. 



■t Owen, and Valenciennes, loc. cit. 



■> Set- fVasner, Icon. zoot. Tab. X.VIX. iig. 32 

 {Loligo), and Firussac, loc. cit. (Loligo, Loli- 

 gopsis, Onychoteuthis, Sepiola, and Sepioteu- 

 this). 



I cannot Iiere omit speaking of the remains of an 

 antediluvian animal, which, under the name of 

 Aptychus, has much engaged the attention of pa- 

 laeontologists, and, up to the present tune, been the 

 object of discussion. 



Some have regar<led it as the operculum of an 

 Ammonite or of another MoUusk {Riippe/l, Abbild. 

 und Beschreib. eiiiig. Versteiner. von Solenhofen, 

 1829, and Voltz, in the Neuen Jahrbuch fur Min- 

 eralogie, &c., 1837, p. 304, 4:32) •, others as a shell 

 of a bivalve {H. von Meyer, in the Nov. Act. 

 Acad. Nat. Cur. XV. pt. II. p. 12.5 and in the 

 .(ahrhuch f. Mineral. &c. I80I, p. 391) ; and oth- 

 ers, finally, as an internal shell of one of the Ceph- 

 alopoda {Coquand, in the Bull, de laSoc. Geol. de 

 France, XII. 1840-41, p. 376). 



This last oijiuion is undoubtedly the correct one. 

 As for myself, I am able to pei-ceivein the different 

 species of ,.//;<i/cAh.? only shells v. hose shaft is abor- 

 tive, and the wings e.xcessively develojjed. I was 

 therefore (juite surprised to hear my colleague, .//- 

 IT under Hraun, express himself in a conversation, 

 lliat, "after all, Uie animal cdled Ap^tychus 



might well have been the male of certain Ammo- 

 nites." If the relations of the Hectocotyli to cer- 

 tain Octopoda are borne in mind, the idea of 

 Braun, that there have existed Ammonites, the 

 males of which are quite different in form from the 

 females, certainly merits much consideration. For 

 the males of these animals were, perhaps, abortive 

 hke those of Ars^onauta and Tremoctopus, and 

 obliged, therefore, to shelter themselves in the man- 

 tle of their females, and this would explain why it is 

 that the specimens of Aptychus are so often found 

 at the base of the first chamber of Ammonites. 



Judging from the form of the shell, the bodies of 

 these animals must have been very large. There 

 will be an additional analogy in favor of this view, 

 if it is proved that the large and flattened animal 

 found by Quoy and Gaimard is really the male of 

 a Nautilus (§ 233, note 3). 



6 The error of Spix (Cephalogenesis, loc. cit. p. 

 33) in comparing it to a rudimentary vertebral 

 column, is still wider. 



7 According to Kotliker (Entwickel. loc. cit. p. 

 72, Taf. V. iig. 45, 46) these c;ilcareous prisms be- 

 gin to be formed in the embryo. 



>i A very detailed description of this Os sepiae 

 has been given by Cuvier (Mem. loc. cit. p. 46), 

 Brandt (Mediz. Zool. II. p. 301, Taf. XXXI. tig. 3, 

 0), tVa^ier (Icon. zoot. Tab. XXIX. fig. 34), and 

 Verussac (loc. cit.). 



