304 WHEELER. [Vok. III. 
(38) and Blochmann (5). The former has described the physical 
structure; the latter, the peculiar bilateral distribution of the 
yolk elements. Though my researches have revealed only 
a few new facts concerning the yolk, I will give them in their 
entirety. 
In the young ovarian egg, 0.5 mm. long, the nucleus is 
surrounded by granular protoplasm in which no yolk has 
developed. In eggs 1 to 2 mm. long the yolk consists of two 
kinds of bodies: transparent fat globules of various sizes, and 
a translucent albuminous substance broken up into distinctly 
outlined masses which are polygonal in form from mutual 
pressure. Beneath the follicular epithelium is a layer of small 
albuminous masses enveloping the interior yolk. This is ata 
time when the large nucleus is disintegrating. By the time the 
egg has reached its full size, the yolk has assumed the highly 
differentiated structure best studied in the oodthecal egg. 
The yolk of a fresh mature egg crushed between the slide and 
the cover glass in its own liquids, or in normal salt solution, shows 
an abundance of different sized highly refractive oil globules, 
and a greater number of distinctly outlined albumen spheres, 
which are polygonal in the intact egg where mutual pressure 
prevents them from taking on the spherical shape which they 
seem to be continually striving to assume. These albumen 
spheres are thin-walled sacs full of a thin liquid in which float 
multitudes of small, irregular granules. Sometimes small oil glob- 
ules are enclosed. That the contents of these sacs is a thin liquid 
is proved by the exceedingly active Brownian movement of the 
irregular granules, a movement which is certainly constant in 
almost all these vitelline bodies in the living egg. But these 
bodies are far from being alike in structure. In some few the 
granules are very minute, closely packed, and exhibit no 
Brownian movement; in others the granules are large and dis- 
tinctly irregular, few in number, and possessed of a tendency to 
unite in flakes which hang suspended in the thin liquid filling 
the sacs. In the great majority of these bodies, however, the © 
mean between these two extremes in structure is maintained. It 
is probable that the granular forms arise from the dense homo- 
geneous bodies by chemical decomposition. This decomposi- 
tion, which is accomplished, as I said above, in the ripe ovarian 
egg, takes place in different parts of the egg in different degrees, 
