No. r.] 



THE ECHINODERM EGG. 



337 



gation is a reticulated vesicle but little smaller than the egg- 

 nucleus. (Contrast Arbacia and Toxopneustes, Fig. 6, Z>.) 



The sperm-nucleus and its amphiaster reach the center of 

 the egg or its vicinity before the formation of the egg-nucleus, 



Fig. 6. Asterias. A, sperm-star dividing during formation of second polar 

 spindle. Sperm-nucleus becoming vesicular. 



B, sperm-amphiaster formed in center of egg. Egg-nucleus without radiations 

 about it advancing to meet sperm-nucleus. Reticular structure of archoplasms. 



C meeting of egg-nucleus and sperm-aster. 



D, conjugation of two nuclei. Sperm-amphiaster converted into first segmenta- 

 tion-amphiaster. 



