CHROMOSOMES AND MITOCHONDRIA ^67 



chromosomes, and generation after generation of 

 such females appear during the summer; but in 

 the autumn, females, whose eggs must be fertilized 

 before they will develop, and males are produced. 

 The chromosomes of these eggs are distributed during 

 maturation as shown in the diagram (Fig. 72). 

 The eggs that develop into the females possess the 

 usual number of chromosomes, but those that give 

 rise to males cast out in the polar body one chromo- 

 some that fails to divide, and hence are provided 

 with one chromosome less than the others. During 

 the maturation of the germ cells of these males two 

 sorts of spermatozoa are formed, one with three 

 chromosomes, the other with only two; the latter 

 degenerate. Therefore, since only one sort of 

 spermatozoa is functional, the fertilized winter 

 eggs are all alike and all give rise to females (stem- 

 mothers) the following spring. 



The chromosome distribution in certain nema- 

 todes resembles somewhat that of the phylloxerans. 

 Here, however, we have to deal with organisms that 

 are peculiar in several respects. Maupas (1900) 

 has shown that in the genus Rhabditis the number 

 of males per 1000 females ranges from 45.0 to 0.15 

 according to the species ; and that these few males 

 do not copulate with the females and hence are func- 

 tionless. Furthermore, the females are not true 

 females, but hermaphrodites. Kruger (1912) dis- 

 covered that in Rhabditis aberrans the nuclei of the 

 spermatozoa did not fuse with that of the egg, except 

 in one instance, but disappeared in the cytoplasm ; 



