44 GENETICS 



the chromosomes that were visible before disappearance, 

 in the following particulars: 



(a) The same number reappears. If the number is 

 changed experimentally, as has often been done, it is the 

 altered number that reappears. 



(b) The chromosomes reappear in the same set of di- 





\^( 





Figure i6. Egg about ready to divide, formed by crossing two 

 species of fish (Menidia by Fundulus). The two kinds of chromo- 

 somes are grouped separately; the long ones are from the Fundulus 

 male, the short ones from the Menidia female. Enlarged from a 

 figure by Moenkhaus (1904). 



verse forms and sizes as before. This is very striking in 

 organisms like Drosophila (figure 7), in which the dif- 

 ferent pairs of chromosomes differ much. In hybrids, often 

 the maternal and paternal sets differ greatly in size and 

 form; each set reappears in its own type (figure 16). 



(c) The chromosomes reappear in the original group- 

 ing and arrangement. When the chromosomes that disap- 



