No. I.] 



THE ECHINODERM EGG. 



335 



for a time after the re-formation of the egg-nucleus, gradually 

 disintegrate, and no trace of centrosome or radiations about 

 the egg-nucleus is subsequently to be found. 



The appearance of the centrosomes within the wall of the 

 vesicle ; the fact that the membrane is clearly fractured behind 

 them ; the minuteness of the archoplasm as they first appear, 

 and its growth as they move outward, indicate that the centro- 



FiG. 5. Asterias. A, origin of two centrosomes in the membrane of the ger- 

 minal vesicle. Archoplasm appearing about them. 



B, a later stage than A. Large archoplasms, with centrosome in each, now be- 

 ginning to separate. 



C, first polar spindle after rotation. Two centrosomes in each sphere. The 

 chromosomes are still irregular in shape. 



D, formation of the egg-nucleus as five small vesicles, surrounded by the archo- 

 plasmic radiations of the second polar spindle. 



E, The sperm of Asterias before penetration, showing tip and middle-piece. 



F, the entrance-cone of Asterias. 



G, beginning of the sperm-star in Asterias. 



