No. 4.] 



BL'LLA SOLITARIA. 



149 



chromosomes have become partly hollow vesicles. A few of 

 the interzonal fibers show at this stage, but they are very faint. 

 In the metamorphoses of the centrosome its attachment to 

 the astral rays is plainly evident ; the old 

 rays can sometimes be seen in a stage 

 younger than the one shown in Fig. 11, 

 when the new rays have already begun to 

 form and are attached to the central corpus- 

 cle. I believe that the rays of the first polar 

 spindle disappear and that the rays of the 



FIG. ?. Prophase second , n1 / 



second spindle rise de now. 



The metakinesis of the second polar spin- 



The chromo- 



m.uuration spindle. Wall 

 of centrosome broken in 

 pieces. Central corpuscles . 



connected by a spindle, die takes place very rapidly. 



New cortical zone form- SQmQS elon ~ ate divide transversely, and as 



ing. Chromosomes are J 



partly hoiiow. A few in- they move toward the poles, they assume a 



terzonal fibers are present. . . , 



roundish form, and change into vesicular 

 bodies which fuse to form the female pronucleus. During the 

 time when they are fusing, the rays can be traced directly 

 into the areas immediately surrounding them. In the stage of 

 anaphase as represented in Fig. 5, the centrosome is evident, 

 although it does not stain as deeply as in Fig. 4. Immediately 

 after this stage the centrosome disappears and the cortical 

 zone enlarges and completely surrounds the 

 female pronucleus ; later both male and 

 female pronuclei come to lie in this clear 

 area. A single centrosome passes off with 

 the second polar body, which is much smaller 

 than the one given off in the first polar body 

 (Fig. 4). 



, . . . . ., FIG. 4. Anaphase second 



The eggs of this species are not especially maturation spind i e . Cen . 

 favorable for a study of the problem of f er- trosome at each p le with 



J a single central corpuscle. 



tilization. During all of the earlier stages, The medullary zone takes 



a plasma stain. 



During all of the earlier stages, 

 the sperm head lies completely surrounded by 

 deutoplasmic spheres. I have not been able to make out any 

 continuous clear area about the sperm head during its prog- 

 ress through the egg. In one instance there was a definite 

 clear area about the sperm nucleus after it had nearly ap- 

 proached the female pronucleus, otherwise it was unattended 



