108 



THE THEORY OF THE GENE 



and there are in all about twice as many elements in 

 bivalens as in univalens. This supports the view that 

 there are twice as many chromosomes in one type as 



C 



Fig. 63. 



First and second cleavages of the egg of Ascaris univalens with 

 two chromosomes. In a and b the fragmentation of the two chro- 

 mosomes in one of the cells is shown. In d, three cells show frag- 

 mented chromosomes, while in the fourth cell the chromosomes are 

 intact. The latter gives rise to the germ-cells. (After Boveri.) 



in the other, rather than that bivalens has arisen through 

 the halving of the univalens chromosomes. 



One form of the brine shrimp, Artemia salina, is, ac- 

 cording to Artom, a tetraploid. There are two races, one 

 with 42 chromosomes, the other with 84 chromosomes 

 (Fig. 64). The latter propagates by parthenogenesis. 



