116 THE CHROMOSOMES 



no evidence of any abnormal cytoplasmic behavior 

 which could account for the observed abnormal effect. 



Tennent also has found that when the sea urchin 

 Toxopneustes (?) is crossed to Hipponoe (^) no 

 loss of chromatin occurs, and the larvae are predomi- 

 nantly paternal, but in the reciprocal cross (Hipponoe 

 ? by Toxopneustes ^) some of the chromatin is 

 eliminated and the larvae are more like the maternal 

 type. 



Some experiments by Herbst also have an impor- 

 tant bearing on the question. The eggs of Sphsere- 

 chinus were put into sea water to which a little 

 valerianic acid had been added. This is one of the 

 recognized methods of starting parthenogenetic de- 

 velopment. After five minutes the eggs were taken 

 out and put into pure sea water to which sperm of 

 Strongylocentrotus was added. The sperm fertilized 

 a few of the eggs. The eggs had already begun to 

 undergo some of the changes that lead to develop- 

 ment. The belated sperm failed to keep pace with 

 the division so that the paternal chromosomes did 

 not reach the poles of the egg before the egg chromo- 

 somes reformed their nuclei (Fig. 40). In conse- 

 quence, the paternal chromosomes formed a nucleus 

 of their own that came to lie in one of the cells formed 

 by the division of the egg. As a result one cell had a 

 maternal nucleus and the other had a double, paternal 

 and maternal, nucleus. In later development the 

 paternal nucleus became incorporated with the 

 maternal nucleus of its cell. Embryos were found 

 later, in the cultures, that were on one side maternal 



