STRUCTURE AND FUNCTION IN MAMMALIAN EGGS 



97 



immediately surrounding cells are anchored to the egg by processes 

 that ramify, forming a network on the surface of the zona, and, as 

 already noted, extend through the zona to make contact with the 

 vitellus (early descriptions were given by Heape, 1886, and Fischer, 



Fig. 74 



Rat egg surrounded by cumulus oophorus; follicle cells embedded 

 in a hyaluronic-acid matrix. X 125. 



1905). While there is no doubt that the contact is real, it is empha- 

 sized that there is no evidence of cytoplasmic continuity between 

 follicle-cell process and vitellus (Chiquoine, 1959, i960; Sotelo and 

 Porter, 1959). It has long been maintained that the follicle cells 

 have a nutritive function in relation to the oocyte; direct evidence 

 for the transfer of lipid material has been obtained by Wotton and 

 Village (195 1) in the ovary of the kitten. The cells are held together 

 partly by intercellular attachment and partly, especially in the 

 periphery of the cumulus, by the matrix. The layers of follicle cells 

 nearest the egg are much more densely packed and present a distinc- 

 tive radial pattern, forming a structure known as the corona radiata 

 (Figs. 74 and 75). During pre-ovulatory maturation and as time 

 passes after ovulation, the follicle cells show degenerative changes 

 and tend to disperse: the processes are withdrawn from the zona 

 pellucida and the cells migrate out of the matrix. Thus, in rats and 

 mice that have not been mated, it is possible to find, on the second 

 day after ovulation, eggs bearing a mass of matrix about them 

 which is almost or completely free of follicle cells. Generally, 

 however, in unmated animals, the entire cumulus breaks down 



