ZOOLOGY — YATSU. 25 I 



Yatso, N», Columbia University, New York, N. Y. Grant No. 268. Experi- 

 mental study of the Nemertine egg. (For previous reports see Year Book 

 No. 3, p. 144, and Year Book No. 4, p. 288.) $1,000. 



Abstract of Report. — Under this grant Dr. Yatsu has continued at the 

 Naples Zoological Station (January to June, 1906) the investigation which 

 was begun in the summer of 1905. While at Naples most of his time was 

 devoted to the analytic experiments on the egg of Beroe. These led to 

 several interesting conclusions, among which may be mentioned the follow- 

 ing : In the &^g of Beroe the ctenoplasm is not definitely localized before 

 fertilization, nor, perhaps, immediately after. At the 8- cell stage the cteno- 

 plasm is not equally distributed in all the cells, the corner cells containing 

 usually a larger quantity. The third cleavage of the egg of Beroe is, there- 

 fore, qualitative, as in the egg of most forms. Incidentally he studied also 

 the mechanism of cell-division in the egg of Beroe. He cut the egg during 

 the first cleavage at different periods and along different planes, and he 

 studied the behavior of the " cleavage-head." This is the first instance in 

 which cutting experiments were employed for this purpose, and he believes 

 that his results offer at least a clue to the final solution of the problem of the 

 mechanism of cell-division. He also studied the early cleavage stages of 

 both the trifoil and ring embryos of Cerebratulus marginatus to determine 

 the seat of the cleavage factors. His results will be published in a series of 

 papers during the coming academic year. 



