-~I 
Cuap. IL TRANSFORMATIONS OF THE YOLK. 51 
there cannot be the least doubt that the faint, thin line (Pl. 9a, fig. 33b) which 
presses closely upon the dark contour of the mesoblast is the wall of the ecto- 
blast; for, even were it not possible to follow with the greatest ease the gradual 
diminution of distance between the two approaching surfaces until contact ensues, 
the action of water, which bursts and peels off the outer membrane, would alone 
serve to prove its existence. 
This fillmg of the ectoblast by the mesoblast is not a feature peculiar to fecun- 
dated eggs found in the oviduct, although it belongs in a great measure to that 
condition of the ovum; for its beginning has been noticed (Pl. 9a, fig. 33a, 33b) 
in one egg, taken from the oviduct of a female known to have been kept from 
the male during a whole year. But, just as segmentation of the yolk proceeds 
to a certain extent in the unfecundated eggs of some animals, so here the filling 
of the ectoblastic cell may occur as a phase continued up to a limited amount 
of the yolk; beyond which, however, the stimulus of fecundation is necessary, in 
order that the process may go on throughout the whole vitelline mass. 
But there is a further change, in the nature of the yolk cells, which belongs 
exclusively to the eggs found in the oviduct; and that is the sudden multiplication 
of the number of the entoblasts, (Pl. 9a, fig. 1, 2a, a, 6, ec, 39d, 39e,) amounting, 
in some cases, to hundreds in each mesoblast, and, in most instances, still preserving 
their rounded form. From what we have sometimes seen in fecundated eggs 
where more than half the yolk cells were totally destitute of entoblasts and the 
remainder for the most part faintly entoblasted, as if these waxy masses were deli- 
quescing, we have good reason to believe that this last feature in the life of 
the entoblast is brought about by a total renascence of entoblasts, after the plan 
of their first appearance in young ovarian eggs, and not by any subdivision of 
each crystalloid body into several smaller ones. That this novel conduct of these 
bodies is intimately connected with the genesis of the embryo there is abundant 
proof in the fact of its simultaneousness with another still more remarkable and 
most important phenomenon, hitherto unsuspected as playing a part in the life of 
the yolk cell of any animal, namely, a self-division of the mesoblast. 
How long before the segmentation of the yolk this process commences has not 
been established; but certainly it may take place without the last fecundation, since 
it was observed in eggs that had not been permeated by this quickening influ- 
ence within a year (Pl. 9a, fig. 33). This may readily be proved by confining the 
females apart from the males during the breeding season, and opening the eggs 
just as they enter the oviduct, when it may be seen that subdivision of the 
mesoblast has proceeded to a certain extent without the help of any recent stim- 
ulus. In such eggs, this selfdivision of the mesoblast was noticed and recorded 
oo” 
as the earliest observed occurrence of this peculiar phenomenon. This is enough 
