2 THE OOCYTE 



erate completely before any definitive cells are formed. In the 

 latter case the oocyte would arise from the germinal epithelium. 

 Some recent studies on this problem include those of Vincent 

 and Dornfeld (1948), Everett (1945), and Jones (1949). An 

 excellent review of the problem of germ cell origin is given by 

 Nelsen (1953). 



The other aspect of the general problem of the development 

 of the oocyte is that of its differentiation and growth into the 

 mature egg. For the purposes of this discussion, it is convenient 

 to define three general areas of influence on the developing oo- 

 cyte. Two of these might be called external, namely, the contri- 

 butions to the developing egg cell by the surrounding circulatory 

 fluids and the contributions to the oocyte by surrounding cells. 

 The third area is the effects of the oocyte nucleus on the develop- 

 ment of its own cytoplasm. 



Considerable information is now available regarding the con- 

 tributions of the circulatory media to the developing egg. Clas- 

 sically, the yolk in avian eggs has been considered to be derived 

 from large molecules carried in the circulation (Romanoff and 

 Romanoff, 1949). Probably the most clear-cut demonstration of 

 the transfer of blood proteins to the egg is that of Telfer ( 1954 ) . 

 He found an albumin-like, antigenic protein present in very high 

 quantities in the blood of female Cscropia during the pupal stage. 

 He was then able to demonstrate conclusively that this protein 

 was transferred to the yolk of developing egg cells. Immunologi- 

 cal similarities between the yolk and adult blood proteins have 

 been detected in vertebrates ( Nace, 1953 ) , and this suggests that 

 in toto transfer of protein ( or at least of specific combining sites ) 

 occurs in these forms as well. In his general review of the devel- 

 opment of immunological properties, Tyler (1955) pointed out 

 that there is evidence that similarities exist between blood pro- 

 teins and both the ground substance and the formed elements of 

 the egg cytoplasm. Considerable importance must be attached 

 therefore to the contributions of the circulatory fluids to the de- 

 velopment of the oocyte. 



The effects of the surrounding cells on the oocyte are varied. 



