130 D. H. TENNENT, 



difterentiation and separation of the cleavage centers had gone 

 on to a considerable extent before the additional spermatozoon had 

 entered the egg. Here the two amphiasters are seen side by- 

 side. In Text Fig. i what may possibly be sperm tails are seen 

 lying within a fertilization cone, although the entrance of the tail 



Fig. I. Toxopnenstes egg X Moi7-a sperm. (Drawn to same scale and re- 

 duced slightly more than are plate figures.) Segmentation nucleus dividing. Extra 

 sperm nucleus in prophase. 



in the fertilization of the echinoderm egg is contrary to the gen- 

 eral belief. 



These cases ought to prove of interest in further investigation 

 along the lines laid down by Boveri in his recent contribution on 

 dispermic sea urchin eggs (Zellen-Studien, Heft 6). 



