TRIPLOIDS 137 



The hybrid between the first two species has 59 chromo- 

 somes (30-|-29). "\A^ien the germ-cells of the hybrid 

 reaches the maturation stages no union takes place be- 

 tween the chromosomes. At the first maturation division, 

 each of the 59 chromosomes splits into daughter halves. 

 Each daughter cell receives this number. At the second 

 maturation division many irregularities occur. The chro- 

 mosomes split again, but the halves often fail to separate. 

 Nevertheless, the male is partially fertile and, as the 

 result shows, some of his germ-cells contain the full num- 

 ber (59) chromosomes. The F^ female is sterile. 



If the Fi male is back-crossed to a female of one of the 

 parent species, to anachoreta, for example, whose ripe 

 eggs contain 30 chromosomes, the second hybrid has 89 

 chromosomes (59+30), and is therefore a hybrid trip- 

 loid. These Fo hybrids resemble closely the F^ hybrids. 

 They have two sets of anachoreta chromosomes and one 

 set of curtula chromosomes. They are, in a sense, per- 

 manent hybrids, although in each generation only half of 

 their chromosomes conjugate. For instance, in the ripen- 

 ing of the germ-cells of these 89 chromosome hybrids the 

 double set of anachoreta chromosomes (30-f30) conju- 

 gates, the 29 curtula chromosomes remain single. The 

 former separate at the first division, the latter divide, 

 giving 59 to each cell. At the second division all 59 chro- 

 mosomes divide. The germ-cells contain, therefore, 59 

 chromosomes and are diploid. As long as back-crossing 

 continues it should be possible to produce triploid indi- 

 viduals. While under controlled conditions it might be 

 possible to maintain a triploid line in this way, it is not 

 probable, owing to the sterility of the offspring resulting 

 from irregularities in the spermatogenesis of the hybrid, 

 that under natural conditions a permanent triploid race 

 could be established.^ 



1 The account in the text has been intentionally somewhat simplified. In 



