M. Ussow’s Zoologico-Embryological Investigations. 217 
layer, and of the cylindrical cells of the inward-bent upper 
germ-lamella, which therefore seems to play the part of the 
intestino-glandular layer of the embryos of other animals, 
representing, I believe, the introverted part of the upper 
lamella from which the intestinal cavity is formed in Amphi- 
oxus*, the simple Ascidiat, and some Ccelenteratat, Brachi- 
opoda§, Vermes||, &c. 
At no single stage of development of the Cephalopod em- 
bryo is the nutritive vitellus in any way directly connected 
with the cavity of the intestinal tract, which is completely 
separated from it, as, indeed, has already been remarked by 
Kdlliker/ and Metschnikoft**, in opposition to the erroneous 
statements of older investigatorstt. At the close of the second 
period the inner nutritive vitellus has the form of a cylinder, 
from which issue three processes. ‘The inferior, sharp process 
is, as previously, imbedded in the mantle; whilst the two 
sickle-shaped lateral processes penetrate into the cephalic lobes 
behind the eyes, beneath the optic ganglia. The nutritive 
vitellus passes out of the yelk-sac into the embryo through a 
cylindrical, gradually narrowing canal formed by the coales- 
cence of the cephalic lobes ; it is situated between the cesopha- 
gus, the ganglion pedale, and the ganglion viscerale. During 
the whole period of development, the whole mass, both of the 
inner nutritive vitellus and of the outer nutritive vitellus 
(which is continually passing into the embryo), is gradually 
absorbed by the cells of different organs and tissues in contact 
with it. 
This short exposition of the results of my tedious investi- 
gations (upon living embryos and sections of them of different 
kinds) of the development of the alimentary apparatus of the 
Cephalopoda contradicts in all points the erroneous opinion of 
Kolliker tf, that the intestinal tract originates as a solid cord, 
in which cavities are only produced subsequently, and con- 
firms the accurate statements of Metschnikoff §§ as to the pro- 
* Mém. de l’Acad. de St. Pétersb. tome xi. pl. i. fig. 6, and pl. ii. 
fig. 20. 
“+ Ibid. tome x. pl. i. figs. 10, 16. 
{ Gotting. Nachr. 1868, p. 154 ef segg. Observations on the Develop- 
ment of the Ceelenterata (in Russian), 1875, pls. ii., ili., iv., vi. 
§ Observations on the Development of the Brachiopoda (in Russian), 
1874, pl. i. figs. 3, 10. 
|| Mém. de ’Acad. de St. Pétersb. tome xvi. pls. i, vi. See also the 
above-cited memoir of Bobrezky’s, pl. i. figs. 1-8. 
q Loc. cit. p. 86. 
** Loc, cit. p. 64. 
tt Van Beneden, Joc. cit. p. 8; Delle Chiaje, Mem. 2nd edit. tome i. 
. 40. 
; tt Loe. cit. p. 93. §§ Loe. cit. pp. 58, 67. 
