274 § 2385. 
THE CEPHALOPODA. 
Spirula,® 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, surrounding the spiral portion of the shell. With all the 
Nautilina, there is another prolongation in the form of a membranous 
tube, or Sipho, 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 witha 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 alance. 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 
surface; 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, transversely-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.© 
8 De Blainville, Ibid. p. 18, Pl. I. fig. 6, A-F. 
4 Owen, and Valenciennes, loc. cit. 
5 See Wagner, Icon. zoot. Tab. XXIX. fig. 32 
(Loligo),and Férussac, loc. cit. (Loligo, Loli- 
gopsis, Onychoteuthis, Sepiola, and Sepioteu- 
this). 
I cannot here 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 time, been the 
object of discussion. 
Some have regarded it as the operculum of an 
Ammonite or of another Mollusk (Rippe/1, Abbild. 
und Beschreib. einig. Versteiner. von Solenhofen, 
1829, and Voltz, in the Neuen Jahrbuch ftir Min- 
eralogie, &c., 1837, p. 304, 432) ; others as a shell 
of a bivalve (H. von Meyer, in the Nov. Act. 
Acad. Nat. Cur. XV. pt. Il. p. 125 and -in the 
Jahrbuch f. Mineral. &c. 1831, p. 391); and oth- 
ers, finally, as an internal shell of one of the Ceph- 
alopoda (Coqguand, in the Bull. de laSoc. Geol. de 
France, XII. 1840-41, p. 376). 
This last opinion is undoubtedly the correct one. 
As for myself, I am able to perceive in the different 
species of Aptychus only shells whose shaft is abor- 
tive, and the wings excessively developed. I was 
therefore quite surprised to hear my colleague, 4l- 
ezxander Braun, express himself in a conversation, 
that, “after all, the animal called Aptychus 
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 
like those of Argonauta and Tremoctopus, and 
obliged, therefore, to shelter themselves in the man- 
tle of their females, and this would explain why itis 
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 itis 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. 
83) in comparing it to a rudimentary’ vertebral 
column, is still wider. 
7 According to Koéliker (Entwickel. loc. cit. p. 
72, Taf. V. fig. 45, 46) these calcareous prisms be- 
gin to be formed in the embryo. 
8 A very detailed description of this Os sepiae 
has been given by Cuvier (Mém. loc. cit. p. 46), 
Brandt (Mediz. Zool. II. p. 301, Taf. XXXI. fig. 3, 
6), Wagner (Icon. zoot. Tab, XXIX. tig. 34), an 
Ferussac (loc. cit.). 
