6l8 GRIFFIN. [Vol. XV. 



tri-lobed, as described by Stauffacher ('93), in Cyclas. The 

 Nebentheil varies in appearance, according to the fixing-fluid 

 employed. After picro-acetic it is large and clear, about three 

 or four times the diameter of the Haupttheil, and contains a 

 bunch of granules staining black with haematoxylin and red 

 with Auerbach's fluid. After sublimate acetic, and occasionally 

 also after picro-acetic, it is larger, bordered by a denser and 

 more deeply staining zone of the nuclear reticulum, and is filled 

 with a finer and sparser reticulum, which shows even greater 

 affinity for plasma stains than does the nuclear reticulum. 

 From the accounts of numerous authors, it would appear that 

 this latter appearance represents more nearly the normal con- 

 dition, and that the bunch of granules is an artifact. 



In the living egg the two portions of the nucleolus appear as 

 two spherical bodies, but slightly different in texture. Com- 

 parison with sections plainly corroborates Flemming's obser- 

 vation that the Nebentheil is more or less swollen by reagents. 



VI. The Centrosome. 



In the earliest condition observed, the polar asters, with their 

 minute dark-staining focal granule or centrosome, have already 

 attained their maximum divergence, and their ingrowing rays 

 commence to break through the wall of the germinal vesicle 

 (PI. XXXIV, Fig. 48). 



As in Thalassenia, a large part of the nuclear skein is thrown 

 out into the cytoplasm, where it undergoes a change in staining 

 power similar to that in Thalassenia ; but instead of becoming 

 diffused throughout the egg, as in the latter form, it here 

 generally sinks into an irregular black mass on the edge of a 

 vacuole (PI. XXXIV, Fig. 50). 



During metaphase or later, the centrosomes divide (PI. 

 XXXIV, Fig. 52) and, rapidly diverging, leave in their path 

 a grayish rod-like streak (centrodesmus) which may possibly 

 be the remnant of the cloudy area seen in earlier stages (PI. 

 XXXIV, Fig. 50). The outer two soon degenerate, while the 

 inner pair, gathering the rays about them in two asters, give 

 rise to the second polar spindle. This, receiving the inner 



