$ 261. THE CEPHALOPODA. 299 
of these halves is also divided, and so on, forming four, eight, &c., segments, 
each resembling a more and more acute triangle, with a converging apex, 
while its base is directly continuous with the remaining vitellus. After a 
certain number of segments have been formed by these longitudinal divisions, 
transverse furrows are seen separating the apices of the segments, and 
forming, at first, in the centre of the eminence, a ring composed of eight to 
sixteen portions; but finally, from a further segmentation in both dirce- 
tions, these furrows become a mass of increasingly smaller and more 
numerous parts.” 
This portion of the vitellus, which, during this time, has also been devel- 
oped at its periphery, is changed into a blastoderma composed of two layers. 
Upon this blastodermal membrane several folds appear, which are the first 
traces of the future embryo, viz. first, a median, uneven fold or rudimenr 
of the mantle, and then two others, lateral, which ultimately form the eyes. 
Between these three folds are placed two others which become the two lat~ 
eral halves of the funnel. Subsequently, the folds of the branchiae and arms 
appear; and among these last the two belonging to the ventral surface are 
first seen. Still later, the folds of the eyes and arms, and their surrounding 
parts, become more and more prominent upon the vitelline mass, thus 
forming the cephalic portion of the embryo. From this last, opposite the 
vitellus, the fold of the mantle is sketched as the future posterior portion of 
the body. The general form of the animal may, therefore, be recognized 
very early, although the cephalic portion quite exceeds that of the mantle. 
At the posterior or dorsal surface of the cephalic portion, the mouth 
appears, first as a semilunar depression, and the internal layer of the blas- 
toderma gradually extends from the border of this portion over the whole 
vitelline mass, producing, finally, a true vitelline sac. The external surface 
of this is covered with ciliated epithelium which gradually spreads over the 
other parts of the embryo, such as the lobes of the head, the arms, the eyes, 
and the mantle, while that of the branchiae, and the funnel, the halves of 
which have then united, is never ciliated. : 
Of the Cartilages, the articular and cephalic are the first developed. The 
internal shell, the nervous system, the heart with the vascular and respi- 
ratory systems, the digestive canal and its appendages, and the ink-sac, are: 
formed successively, and may be easily seen at the termination of the 
embryonic life, when, also, are found some chromatic cells. 
As to the vitelline sac, it should be remarked that it never communicates 
with the intestinal canal, as has hitherto been supposed.” The cephalic 
portion, which always extends upon this sac, embraces a part of it, so that 
it is divided by a constriction into an internal and external portion, the 
former of which extends even into the cavity of the mantle. The con- 
stricted portion is gradually elongated, and finally becomes a long, very 
narrow canal, extending from the cephalic extremity to the side of the 
2 See Kolliker, loc. cit. p. 17, Taf. I. 
p. 379, and Maravigno, Ann. d. Se. Nat. VIL.. 
8 With Loligo, the vitelline sac and its ciliated 
1837, p. 174. 
epithelium are formed quite early ; while with Se- 
pia, they do not appear until the embryo and its 
different organs have become quite large. With 
the first, the embryos have rotatory movements, but 
with the second this is not the case (Kédliker, loc. 
cit. p. 54). 
4 With Argonauta, the external shell is formed 
while the embryo after its escape from the egg, is 
still persistent in the spawn inside the shell of its 
parent ; see Power, in Wiegmann’s Arch. 1845, I. 
5 Most of the earlier anatomists were led into. 
error from the tenuity of the canal of communica- 
tion, and the difficulty of its examination. They 
supposed that the external vitelline sac communi- 
cated with the cesophagus and stomach, by this 
canal; see Carus, loc. cit. Taf. II. fig. 27 (Loli- 
g0); Cuvier, loc. cit. Pl. VIII. fig. 9; Duges, loc. 
cit. Pl. V. fig. 3 (Sepia) and Van Beneden, loc. cit. 
Pl. I. fig. 13 (Sepiola). Kélliker was the first to 
view it co-rectly (loc. cit. p. 86, Taf. IV.). 
