244 LILLIE. [Vol. XVII. 



to some slight difference in the constitution of the cytoplasm 

 in the two cases. That such different courses of events can 

 yet lead to the same typical result indicates a most remark- 

 able power of self-regulation of the entire ovum, and at the 

 same time demonstrates that the mechanical processes of 

 spindle and aster formation are not the primary factors in 

 determining the position of the maturation spindles. 



The later history of the sphere and centrosomes of the second 

 maturation spindle is shown in Figs. 22, 23, PI. XXV, and in 

 Fig. 32, PI. XXVI. During the anaphase the inner sphere 

 becomes hollowed out in the interior, just as in the correspond- 

 ing phase of the first maturation spindle ; and, as there, so 

 here, the wall of the sphere becomes the central area of attach- 

 ment of the rays, the centrosome itself being united to the wall 

 of the sphere by a few fibers, which are independent of the aster 

 proper. In the stage of Fig. 23, PI. XXV, the centrosome 

 is invariably placed excentrically within the sphere. What the 

 meaning of this may be I have no idea. The centrosome does 

 not divide during the anaphase of the second maturation 

 division. But in the stage of PL XXVI, Fig. 32, the sphere 

 has enlarged considerably, and its interior is occupied by a 

 reticulum, at the nodes of which are a number of microsome- 

 like bodies. 



The accessory aster. — Shortly after the metaphase of the 

 second maturation spindle an accessory aster is formed in the 

 egg. It usually arises quite near the center of the Q.g% and 

 bears no fixed relation either to the maturation spindle or 

 the sperm-nucleus ; the center of the aster is occupied by an 

 exceedingly minute centrosome. The latter divides and a 

 small amphiaster is formed (PI. XXV, Fig. 28) which entirely 

 disappears before the stage of PI. XXV, Fig. 23. 



What is the significance of the accessory aster } Is it simply 

 due to a renewal of activity of the sperm-centrosomes which 

 disappeared a cell generation before, or is it an entirely new 

 formation } I do not believe that it has anything to do with 

 the original sperm-asters for several reasons : in the first place, 

 there are two sperm-centrosomes, and the accessory aster is 

 at first single and later divides ; secondly, the usual place of 



