Basis of Sex Determination 213 



female. How can we reconcile the facts of hermaphro- 

 ditism with the chromosome theory of sex determina- 

 tion? RJiabdonema nigrovenosum, a parasite living in 

 the lungs of the frog, is hermaphroditic, but its eggs 

 produce not a hermaphroditic generation but one with 

 the two separate sexes; this generation is not parasitic 

 and lives in the soil. The generation produced by these 

 separate males and females gives rise again to a her- 

 maphrodite which migrates into the lungs of the frogs. 

 According to Boveri and Schleip 1 the cells of the her- 

 maphrodite have twelve chromosomes. It produces two 

 types of spermatozoa with six and five chromosomes 

 respectively (one-half of the cells losing one chromosome 

 which is left at the line of cleavage between the two 

 cells) ; and one type with six chromosomes. In this way 

 separate males and females are produced by the her- 

 maphrodite, females with twelve and males with eleven 

 chromosomes. 



The males produce again two kinds of spermatozoa, 

 male and female producing, but the male-producing 

 spermatozoa become functionless. This fusion of the 

 other spermatozoon containing six chromosomes with 

 an egg having six chromosomes leads again to the for- 

 mation of the hermaphrodite with twelve chromosomes. 

 It is obvious that in this case the cause for the her- 

 maphroditism is not disclosed. If chromosomes have 



1 Boveri, Th., Verhand. d. phys.-med. Gesettsck. Wurzburg, 1911, 

 xli., 85. Schleip, W., Ber. d. naturf. Gesellsch., Freiburg i. Br., 191 1, xix. 



