THE CHROMOSOMES 149 
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 Hipponoé (¢) no 
loss of chromatin occurs, while reciprocally some or 
even all of the paternal (?) chromatin is eliminated, 
but the character of the larve in the two cases does 
not furnish a basis for discrimination as regards the 
effects due to elimination. 4 
Some experiments by Herbst also have an impor- 
tant bearing on the question. The eggs of Sphere- 
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 
