136 THE THEORY OF THE GENE 



chromosomes at maturation by means of the character- 

 distribution in the progeny. It has also been possible to 

 study the crossing-over, and to determine that the chro- 

 mosomes mate in threes. 



In true triploid Drosophilas there are three sets of 

 ordinary chromosomes and three X-chromosomes also. 

 If, on the other hand, there are only two X-chromosomes 

 present the individual is an intersex. If only one X is 

 present the individual is a supermale. These relations 

 are as follows : 



3a+3X=triploid female 



3a4-2X=intersex 



3a+lX=supermale 



In bisexual animals another triploid is known in an 

 embryonic stage. Females of the bivalens variety of the 

 threadworm Ascaris have been reported whose ripe eggs 

 with two chromosomes have been fertilized each by a 

 spermatozoon of a univalens variety with one chromo- 

 some. These eggs produce embryos with three chromo- 

 somes in each cell. Since the embryos escape before their 

 own germ-cells mature, the most significant feature of 

 their chromosome behavior, namely, union during con- 

 jugation, has not been observed, for as yet no adult trip- 

 loids of Ascaris have been reported. 



Triploids have been produced by crossing diploid spe- 

 cies and back-crossing the hybrid (that has diploid germ- 

 cells owing to the failure of conjugation and reduction) 

 to one of the parental stocks. The experiment was carried 

 out by Federley with three species of moths with the fol- 

 lowing chromosome numbers. 



