(Su) 
Cuap. I. DEVELOPMENT OF THE YOLK CELLS. 47 
After this comes a great change, not only in the yolk cells, but throughout 
the whole organism of the egg. The entoblasts begin to decrease in number, 
and lose their angularity (PI. 9, fig. 7e, Te); the mesoblast, as we have before 
mentioned, encroaches upon the hyaline area of the ectoblast; and, to crown the 
whole, the Purkinjean vesicle changes its complicated cellular structure (Pl. 9, fig. 
5a, 5b, 5c) into one which is almost perfectly homogeneous, (Pl. 9, fig. 7a, 7b,) 
and this too without the least sign of any new or external influence, so far as 
we have been able to penetrate the process of this development. 
But, to return to the continuance of the entoblastic changes, let us first note 
the numerical decrease of the waxy crystalloid bodies as the primary indication 
of any signal divergence from the hitherto uniform line of conduct; and, secondly, 
the rounding off of their angles. It is a matter of some doubt as to whether 
the existence of a few entoblasts in each cell is owing to the actual decrease in 
the number of each cluster, or to the total dissolution of the ectoblast, mesoblast, 
Now if the lat- 
ter supposition be true, it is hardly possible, that, durmg the evanescence of these 
and entoblasts, and the regeneration of new ones in their stead. 
bodies, some should not have been found in a transitory state, either a mesoblast 
without an ectoblast around it, or an ectoblast without mesoblast, or an entoblast 
totally exposed, or a mesoblast without an entoblast; and, since no such changes are 
noticed, we are forced to adopt the former conjecture, which has at least a certain 
amount of evidence in its favor. This we will attempt to support by referring to 
an ege (Pl. 9, fig. 7) a little older than the last, in which, amid cells as yet con- 
taining angulated entoblasts, (Pl. 9, fig. 7f 7g,) may be seen, here and there among 
the largest, some cells in which the sharp edges of the entoblasts have begun to be 
rounded (fig. 7c, 7e) and the total number of entoblasts has considerably decreased, 
though they still hold their angular features; but soon these angles are lost and 
superseded by rounded contours embracing irregular but more equal sided masses, 
varying from pyramidal to cubical, (Pl. 9, fig. 8a, A, A, A,) or from oval to spher- 
ical forms (fig. 8a, B, C, C). 
(Pl. 9, fig. 8,) and in which the number of entoblasts may vary from five or six 
In an ege three eighths of an inch in diameter, 
1 Tn view of such a parallelism of changes, we that the mind would fain decide upon. Inasmuch as 
cannot but conceive that there must be some total the egg, at this age, is far from full-grown, but rests 
action, to which each special influence, in the several 
organisms of the egg, is secondary. However, it is 
not so much the presence of such a force, as its na- 
ture and origin, — whether it is inherently an idiosyn- 
crasy of the region in which it operates, or whether 
it is generated by some periodic external agency, 
as for instance the repeated acts of copulation, — 
60 
unspecialized among many of the same size, it cannot 
be advocated that it may be subject to any external 
influence, and that too whilst those a little smaller re- 
main unaffected; and so we must fall back upon the 
former and more probable explanation, and, for want 
of additional facts, leave it, about as in the beginning, 
an unsatisfactory matter of conjecture. 
