458 EMBRYOLOGY OF THE TURTLE. Part III. 
PHCTION 1 
DEVELOPMENT OF THE YOLK. 
In order that the history of the yolk, which follows, may be complete in itself, 
it is advisable to revert to the first appearance of what is afterwards called yolk, 
as the original contents of those particular granule-like cells which eventually 
declare themselves as eggs. 
We have already said, that at first the yolk is a perfectly homogeneous, highly 
refracting, brilliant, yellowish fluid, which gradually loses its density, and becomes 
more transparent and colorless up to a certain age of the egg, when the whole 
begins to appear heterogeneous in its aspect (Pl. 8, fig. 1, p). At this period, 
when the egg is about 5,5, of an inch in diameter, there ensues a great and 
very remarkable change ; the contents of the ege divide into two very differ- 
ent looking portions, (PI. 8, fig. 1, p,) one of which retains the character of 
the stage just passed, (upper part of fig. 1, p,) whilst the other, which is the 
larger, assumes a clear, hyaline, and hardly refractive condition, indicative of a 
greater amount of albumen than in the darker part. 
The germinal vesicle is usually found in the more transparent portion of the 
ego, but now and then it les in the darker region; when in the former it is 
at times difficult to recognize, because its density and that of the enveloping 
medium are so nearly alike’ as to give a very faint difference in refraction. 
Soon after this, when the egg has reached the size of 5,559 of an inch in 
diameter, the homogeneous fluid of the darker side becomes spotted here and 
there with very minute granular vesicles, with dark outlines (Pl. 8, fig. 2, 3, 3a). 
These vesicles are mostly situated near the periphery of that side of the egg; but 
eradually they appear nearer and nearer to the centre, increasing in size at the 
same time, till they occupy the whole field adjoining the hyaline region, (Pl. 8, 
fiz. 4, 5,) when the whole mass presents an opaque, dense, fuscous colored 
and coarsely granulated appearance. There is no constant relation, at any given 
time, between the size of the egg and the amount of light and dark parts, in defi- 
nite proportions to each other. One egg may have its denser region but. slightly 
granular, while that of another of the same size will be filled with granules. The 
same indefinite relation occurs throughout the different parts of the egg, even to 
quite an advanced period. 
But, to return again to the younger stages, we would note the very remark- 
able and sharp, straight line of meeting of the two different portions of the egg, 
