446 R. M. PACE. 



of passing out through the nuclear membrane. The chromatin 

 network is somewhat dense, and it has at its nodes deeply- 

 staining granules, which are similar in their appearance to 

 the original elements of the yolk nucleus, while a faintly 

 staining substance occupies its interstices. 



The germinal vesicle at first grows relatively more rapidly 

 than the egg as a whole, and the chromatin network becomes 

 more attenuated (PL 23, figs. 80-32) ; but this latter fact is 

 probably due rather to the increased size of the nucleus than 

 to any emission of chromatin from it. No further changes 

 take place in the germinal vesicle until after the formation of 

 yolk has been completed, although the irregular contour of 

 the nuclear membrane observed in certain sections (PI. 23, 

 figs. 24, 25) during the period of yolk formation may possibly 

 denote amoeboid movements in connection with the latter 

 process :'such amoeboid movements have been described by 

 Bambeke (1) in the case of the egg of Pholcus phalan- 

 gioides. 



After the completion of yolk formation the chromatin net- 

 work begins to thicken (PL 23, fig. 33), and the substance 

 between its meshes now stains more deeply (PL 23, fig. 34). 

 The nucleolus also becomes relatively very large, and at the 

 same time the nuclear membrane loses its regular outline 

 (PL 23, figs. 34, 35). These processes continue until all trace 

 of the chromatin network has disappeared, and the nucleus 

 stains uniformly throughout (PL 23, fig. 36). At this stage, 

 which is immediately prior to that of the formation of the polar 

 bodies, the nucleus begins to decrease in size relatively to 

 the rest of the egg and becomes amoeboid : the nucleolus is 

 still present. 



The Nature and Function of the Yolk Nucleus. — 

 The term "yolk nucleus" has been applied by various 

 authors to bodies which appear to be totally different in 

 their origin, development, and appearance, and which 

 would seem to have only this much in common, that all 

 have been regarded as being in some way connected with 

 the phenomenon of yolk formation. In the present instance. 



