154 THE CHROMOSOMES 
the fish Fundulus is crossed to another fish, Menidia, 
the two kinds of chromosomes present in the fertilized 
egg can readily be distinguished in later divisions. 
Similar observations have been made for many 
other crosses (Fig. 42) by Morris, Pinney, Hertwig, 
Federley, Doncaster, Rosenberg, etc. Despite the 
fact that the paternal chromosomes are in a foreign 
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Fic. 42.—a, Telophase, rae of an embryonic cell of Fundulus; 6, 
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 
