240 Mr. E. A. Schafer. On Immature Ovarian Ovum [Mar. 18, 



shade off the one into the other. Close to the surface is a thin layer 

 (fig. 10, I) very clear and almost free from granules, or these 

 are of extreme minuteness ; next there is a finely granular looking 

 layer (II), considerably thicker than the last, in the deeper part of 

 which are imbedded the elements of the white yolk (III), which thus 

 forms the third layer, and which passes gradually into the main central 

 substance, or yellow yolk (IV). It is difficult to observe the inter- 

 lacing filaments of which the vitelline substance is in all probability 

 composed : even with the highest powers the superficial layers of the 

 yolk of these larger ova show little more than an appearance of fine 

 punctation. 



Peculiar striated systems of fibres (figs. 12 and 13) are to be seen 

 occasionally in the vitellus of some of the larger ova. They are gene- 

 rally situated near the end or ends (for there may be two such systems 

 in one ovum) of the ovum, and call to mind some of the amphiastral 

 appearances of dividing nuclei. The fibres composing them do not 

 become more darkly stained with . magenta than the rest of the 

 vitellus, but they are very obvious both on account of their peculiar 

 arrangement (each system consisting of two triangular halves diver- 

 ging from a common centre) and on account of the fact that they lie in 

 a substance which is clearer and stains less than the rest of the vitellus. 



In the ovum figured (fig. 12) one of these striated systems is situ- 

 ated in a projection of the vitellus. I draw attention to this because 

 it may mean that the vitellus just at the neck of the projection where 

 the system is situated is in a condition of contraction, and that the 

 appearance described is characteristic of that condition. On the other 

 hand, it is just possible that the figures in question are actually karyo- 

 litic, and derived from some extruded portion of the contents of the 

 germinal vesicle. In this case the phenomenon is probably connected 

 with the precocious formation of polar globules. I say " precocious," 

 because the ovum in question was far from maturity ( 5 ) . 



Membranes of the Ovum. — I have only one remark to make about the 

 external coverings of the bird's ovarian ovum, and it concerns the 

 zona radiata. Waldeyer states that this membrane or layer is derived 

 from cells of the follicular epithelium, and is continuous with their sub- 

 stance ( 6 ). I find on the contrary that in good sections the zona is com- 

 pletely distinct from the follicular epithelium, and its outline is more 

 sharply defined externally than internally (fig. 11, z. r.). Moreover, 

 where the epithelium has accidentally been broken away, portions of its 

 cells do not adhere to the zona, as they would tend to do if their sub- 

 stance were continuous with it. I am inclined with Balfour ( 7 ) to 

 regard the zona radiata therefore as a product of the protoplasm of 

 the ovum. I have not been able to gain any information with regard 

 to the origin of the vitelline membrane which might enable me to 

 decide whether it is a product of the yolk or of the follicular epithelium. 



