1 68 MUNSON. [Vol. XV. 



suspended in a fluid, enters the vacuoles and meshes of the 

 living substance of the egg. 



At the time when the first layer of the egg membrane is 

 formed it is sometimes seen that part of the yolk is not 

 included within the membrane, but is cut off and remains out- 

 side in that portion next to the stalk of the egg (PI. XIV, Fig. 

 22, y.s!). The yolk lying outside of the egg in such cases is 

 often considerable in amount, and resembles in every particu- 

 lar the yolk inside of the egg. Two explanations of this 

 appearance suggest themselves, which, although appearing 

 different, may be essentially the same. In the first place, it is 

 safe to assume that the first layer of the egg membrane arises 

 at the extreme limits of the formed, living substance of the 

 egg. Now it may be suggested that in such cases as those 

 under consideration the amorphous elements of the egg extend 

 beyond the outer limits of the living protoplasm, and thus 

 become cut off when the membrane arises. Or it may be that 

 the yolk granules from the epithelial cells, being prevented 

 from entering by the membrane, accumulate outside, later per- 

 haps becoming dissolved and serving as food. It is suggestive 

 that at this stage in the history of the egg, when the yolk 

 granules from the outside are no longer capable of entering as 

 solid bodies, the cytoplasm of the egg undergoes that peculiar 

 change from an alkaline to an acid state of reaction. 



The yolk spheres appear in their vesicular, clearly defined 

 form only after the egg has been discharged from the follicle. 

 Previous to this event several of the epithelial cells of the egg 

 stalk appear to degenerate and break up into granules that 

 have all the appearances of the yolk granules of the ovarian 

 egg. On the first appearance of the definite yolk bodies they 

 are small. Those first formed increase in size, and thus in 

 somewhat later stages the yolk bodies may sHow many different 

 sizes. Ultimately, however, they all attain to a considerable 

 size and fill the egg completely. There can be no doubt that 

 these yolk spheres originate within the &^z. Their formation 

 appears to be in some way associated with the new mode of 

 nutrition of the egg after its arrival in the ovarian tube. As 

 previously stated, it is here bathed in the secretion of the cells 



