DEVELOPMENTAL HISTORY OF THE MOLLUSCA. 43 
to the yelk from their proliferous surfaces. In fig. 23, Plate 12, a portion of the same 
section, more highly magnified, is accurately represented, showing the cells in various 
stages of incorporation with the yelk, as they pass from the proliferous surface of the 
inner capsular membrane. 
There does not appear to be any room at all for doubting that cells keep on passing 
off from the surface of these folds of the inner capsular membrane into the yelk, just 
as cells keep on passing away as scurf from the surface of the human epidermis. It is 
a very different question as to whether they retain their vitality and individuality after 
passing into the yelk. This question is now one of the very greatest importance in 
embryology generally ; and without discussing the views of Professor His or his oppo- 
nents, who have made the egg of the hen and of osseous fishes their study, I desire to 
draw attention to the facts observed in the case of the Cephalopods Sepia and Loligo. 
Of the cells which pass off or are proliferated into the yelk, so to speak, by far the 
majority are undoubtedly metamorphosed and broken down into a condition chemically 
lower than that of living protoplasm before they have long been there. Hence there 
is not such a wide distinction between this third mode of the egg’s nutrition, which I 
shall call “‘corpuscular,” and the earlier form of inceptive nutrition, which may be 
distinguished as secretional. In the latter a portion of the goblet cell or corpuscle 
was metamorphosed and thrown into the egg-mass; in the former it is a whole cell 
which is thrown in and subsequently metamorphosed. 
The stages of the egg’s nutrition may be thus grouped :— 
iepsape ss lane Oe  Opmotie, 
2nd stage. . . . . Secretional 5 } : 
‘ Inceptive. 
ora stage. 5...” Corpuscular’. ; 
But the question arises whether all the cells which migrate thus in such immense 
numbers into the egg-yelk are equally metamorphosed, and to be regarded as haying 
lost their independent vitality. It is, of course, open to any one to maintain that the 
cells which lose all trace of their nucleus and become irregular, highly refracting 
masses of indefinite outline are yet capable of resuming their original properties as 
protoplasmic corpuscles, and that they are not really degenerated, but only temporarily 
modified. Cells or corpuscles which subsequently appear and take part in the for- 
mation of the tissues may then be ascribed to the retention of individuality and 
protoplasmic properties by the cells proliferated from the inner capsular membrane. I 
believe, however, that corpuscles which have undergone the changes above described 
and indicated in the Plates (Plate 12. figs. 23 & 24) will be considered by most persons, 
as by myself, to have passed irretrievably from the living condition to that of a meta- 
morphic product. Strangely enough, however, as though to prevent our feeling any 
assurance that the survival of such cells in an egg-mixture is rendered quite improbable 
by the facts observed in Sepia and Loligo, we find, both in the fully formed and the 
immature oyarian eggs of Sepia, here and there scattered in the yelk, nucleated cells, 
a2 
