THE CHROMOSOMES 



121 



the fish Fundulus is crossed to another fish, Menidia, 

 the two kinds of chromosomes present in the fertihzed 

 egg can readily be distinguished in later divisions. 

 Similar observations have been made for many other 

 crosses (Fig. 42) by Morris, G. and P. Hertwig, 

 Federley, Doncaster, Rosenberg, etc. Despite the 

 fact that the paternal chromosomes are in a foreign 



Fig. 42. — a, Telophase, division of an embryonic cell of Fundulus; b, 

 telophase, division of an embryonic cell of egg of Fundulus fertilized by 

 sperm of Ctenolabrus. (After Morris.) 



medium they retain their characteristic size, form, 

 and number. The embryos from these eggs are 

 abnormal, and often die, not because chromosomes 

 are eliminated but because the combination does not 

 work out successfully. On the other hand, in hybrid 

 embryos (studied by Herbst, Baltzer, and Tennent) , 

 in which paternal chromosomes are eliminated, they 



