John P. Miinson 319 



from the young germinal vesicle, is also a direct continuation of the 

 cytoplasm of the original oogonia. The cytoplasm being so limited, it 

 is easy to regard the sphere as the most essential part of the cytoplasm, 

 and from the later history of this body in the growing egg, one is almost 

 tempted to infer that a chromosome organically connected with a centro- 

 some and sphere is sufficient to develop a nucleus from the former and 

 cytoplasm from the latter, i. e., a cell, in the present case, the egg. In 

 this early stage, immediately following the reconstruction of the nucleus, 

 (now the germinal vesicle), from the chromosomes of the spindle, it is 

 hardly possible that metabolic processes in the nucleus could be respon- 

 sible, on the one hand, for the central nucleolus-like body in the nucleus 

 of the peripheral (follicle) cells; or, on the other hand, for the accumu- 

 lation, at one pole of the young germinal vesicle, of the slightly granular 

 centrosome and sphere. 



The staining reaction of the chromatin and archoplasm respectively is 

 so different that the origin of the one from the other could not even be 

 suggested by it. The chromatin stains deeply and easily in nuclear 

 stains, the centrosome and archoplasm, on the contrary, are conspicuous 

 chiefly for their resistance to nuclear stains. 



I conclude from the above facts that there are important internal 

 differences between the follicle cells and the oocyte at this earliest stage. 

 The principal difference is the position of the centrosome in the oocyte, 

 which not only gives it a polarity, but also seems to confer on the oocyte 

 the capacity for growth. It is this centrosome and sphere which later 

 grows so extensively by the absorption of food and the formation of yolk 

 in the later stages as can be seen by examining Plate YII. The prob- 

 able function of the nucleus in this later growth is suggested by the 

 origin and history of the yolk-nucleus to be described later on in this 

 paper. 



THE EGG. 



Stages of Growth. — The history of the growing oocyte presents 

 three successive phases, which may be used as landmarks for descriptive 

 purposes. 



The first period extends from the beginning of growth, to the time 

 when the cytoplasm assumes its characteristic granular appearance; at 

 which time, also, the true nucleoli make their appearance in the germinal 

 vesicle. 



The second period extends from the first period to the beginning of 

 true yolk-formation; and the third period covers that period of growth 

 in which the true volk-bodies are formed. 



