MUSEUM OF COMPARATIVE ZOOLOGY. 89 



the zona has become thicker, but they are much finer than in the mature 

 egg. After describing the condition in Acerina vulgaris (p. 18), the 

 following statement is made as embodying the author's idea of what 

 takes place in the formation of the zona. The granulosa cells secrete a 

 substance (Zwischensubstanz), which surrounds the egg, one layer upon 

 another. The pores in this substance arise by the growth into it of the 

 points of the granulosa cells, or plasmatic processes from them. The 

 way in which the author describes the mushroom-shaped villi which 

 surround the micropyle in Gasterosteus shakes one's confidence in this 

 part of his work. It is very probable, he says, that they are derivatives 

 of the granulosa cells. After admitting that they have been described 

 in a masterly way by Kolliker, he gives an interpretation of them that 

 must appear to that author very remarkable. They are nothing less 

 than individual cells (!), each with a nucleus that is stained red in 

 carmine while the cell protoplasm resists for a time the action of the 

 dye. From the base of the cell emerges a thread which can be traced 

 into the zona. Very young eggs possess these appendages, as Kolliker 

 maintained, but they are much smaller, and consist essentially of a 

 nucleus which is attached by a thread and surrounded by a thin film 

 of protoplasm. 



If everything that is stainable is to be called either nucleus or cell 

 protoplasm, then the current notions of what constitutes a cell will 

 have to be abandoned ; that will give room, it is true, for the admission 

 into this category not only of the villi and the yolk cells of His, but also, 

 I fear, of many other structures as well. 



The author's views concerning the villous layer in other cases appear 

 from his account of Coregonus. The granulosa cells send processes into 

 the zona radiata. When they are removed from the immature egg, the 

 zona appears to be covered with small more or less pointed " Zottchen," 

 which are therefore to be regarded as processes of the granulosa. Out- 

 side the zona radiata, Owsjannikow finds in many cases a thin viscid 

 layer, which he suggests is derived from the oviduct in the case of 

 S. trutta, but looks in Lota as though it resulted from the fusion of 

 endothelial [granulosa 1 ?] cells. 



Solger ('85, pp. 330-332) is evidently inclined to bring the villous 

 layer into connection with the presence of intracapsular corpuscles found 

 in the perivitelline fluid. Without committing himself unreservedly to 

 the views of Eimer, — that the villi are simply exuded drops of vitelline 

 substance, — he confirms the statement that they are not of uniform 

 length or shape in the case of Leuciscus rutilus, and says that Eimer 



