480 EMBRYOLOGY OF THE TURTLE. Part III. 
the Purkinjean vesicle’ being much smaller (PI. 9, fig. 6b) than those nearer the 
centre of the ege (fig. 6a); and between these two extremes a gradual increase 
in bulk from the former to the latter is readily traced. This feature holds good 
throughout the succeeding phases of the ovarian egg, even to its full develop- 
ment (Pl. 9, fig. 11d—11g),’ 
that side of the egg where the Purkinjean vesicle is situated. 
About this time, also, there appears a whitening of 
This whiteness 
increases in intensity and breadth as the egg enlarges, till im a full-grown ovum 
it occupies a considerable area. This differentiation of color from the surrounding 
and gradually deepening yellow is owmg to the increasing preponderance of albu- 
mino-oleaginous clear cells (Pl. 9, fig. 5c, 4, lle) around the  Purkinjean vesicle, 
intermixed with the usually larger mesoblasted ones? Again, as the ege comes 
to maturity, the yolk cells increase to an enormous size, (Pl. 9, fig. 11g, 114,) 
their single yellow mesoblasts nearly fill them, and the waxy entoblasts gorge the 
mesoblasts. Thus, by the decrease of the clear space, and the fillmg up of the 
same by the darker and yellow mesoblasts and entoblasts, the whole egg gradu- 
ally receives a deeper and more orange-colored hue, excepting, as we have said 
above, where the space around the Purkinjean vesicle is whitened by the greater 
predominance of cells with homogeneous contents and a white reflection. 
At this time, too, the Purkinjean vesicle has lost its Wagnerian vesicles, and 
presents pretty uniform homogeneous contents, (Pl. 9, fig. 9c, 10c, 11b,) of a highly 
albuminous nature, so clear and dark as to give the surface of the egg the appear- 
ance of having a hole in it (Pl. 9, fig. 4-10; Pl. 9a, fig. 16, 18, 32, 32a). 
is never, not even when the egg is matured, the least trace of a separation of a 
There 
portion of the yolk around the Purkinjean vesicle, to form what is called, in 
the Bird’s egg, the “cicatricula”; on the contrary, as we approach this region, 
1 According to Meckel von Hemsbach, Leuckart, 
Thompson, and others, the region in the vicinity of the 
Purkinjean vesicle of the Bird’s ege is quite deficient 
in the “corpuscles” characteristic of the yellow yolk ; 
the space thereabout and the canal leading to the cen- 
tre of the yolk mass being occupied by bodies quite 
different from those exterior to them in the mass of 
vitelline substance. Yet, from the description of these 
authors, it would appear that the genetic connection of 
these bodies had not wholly escaped them; but that 
they have laid too much stress upon the extremes of 
a graduated modification, which is very similar to that 
which obtains in the egg of Testudinata. 
* See the description of these cells, p. 474. 
* The clusters of cells on the periphery of the 
enlarged Purkinjean vesicle, represented in fig. 5c 
and 11b, and marked 4 around fig. 5c, and 11¢ around 
fig. 11b, are meant to represent a part of the whit- 
As the 
reader may find some difficulty in tracing these refer- 
ened yolk which surrounds these vesicles. 
ences upon the plates, as the cells of the white area 
are represented on the edge of the figures referred to, 
which is their true position, a few more remarks are 
needed. In fig. 5c, the letter 6, which designates these 
cells, may be seen on the margin of a cluster border- 
ing on the left upper side of the Purkinjean vesicle 
which they surround. In the same manner are these 
cells represented in fig. 1le, as bordering the Purkin- 
jean vesicle of fig. 11b, which they surround in the same 
manner as the smaller cells of the preceding figure. 
