W. S. VINCENT 3 



Apparently, they must provide some of the differentiating influ- 

 ences that allow the presumptive oocyte to form an egg, since 

 egg cells are not known to differentiate outside the ovary. A dis- 

 cussion of some of these inducing influences is given by Vincent 

 and Dornfeld (1948). The follicle cells which surround the oo- 

 cyte are usually considered to function in some positive manner 

 during the growth of the oocyte — either by direct transfer and/or 

 fusion of all or part of the follicle cell to the developing egg, or 

 by acting as a transfening system for substances provided by the 

 blood stream. 



In the cases in which the accessory cells contribute directly to 

 the substance of the oocytes^ the accessory cells are known as 

 nurse cells. At times, the egg cell and its associated nurse cells 

 can be shown to have been the offspring of a single parent cell 

 (see discussion in Wilson). Often the transfer of not only cyto- 

 plasm but also nuclear material is observed in the oocyte-nurse 

 cell relationship. (For recent histochemical studies of such rela- 

 tionships see Schrader and Leuchtenberger, 1952.) It seems rea- 

 sonable to assume that the "excess" amount of deoxyribonucleic 

 acid found in the cytoplasm of oocytes may arise from such 

 nuclear transfer (Zeuthen and Hoff-j0rgenson, 1952; Marshak, 

 1953). The nature of the cytoplasmic materials that are trans- 

 ferred to the egg is discussed by Schrader and Leuchtenberger. 

 Where direct transfer of large cellular fragments is concerned, it 

 is obvious that there does exist a mechanism for considerable 

 modification of oocyte development by its cellular environment. 



The existence of transferral mechanisms ascribed to the follicle 

 cells is based primarily on inference. Inasmuch as this cellular 

 layer is interposed between the blood stream and the egg, it has 

 generally been assumed that the follicle cell functions in the 

 transfer of materials to the oocyte cytoplasm. Little experimental 

 evidence is available to confirm or deny the validity of such an 

 assumption. 



The third area of, influence, that of the effects of the oocyte 

 nucleus on its own cytoplasm, has been widely studied. The nu- 

 clear changes which accompany the growth of the oocyte are so 



