206 CHROMOSOMES OF PARTHENOGENETIC FROGS 



Since none of the individuals studied has the haploid number, it 

 is probable that the diploid number is characteristic for the majority, 

 if not for all the parthenogenetic individuals. The diploid number, 

 as well as the similarity in form of the tetrads of the parthenogenetic 

 and normal animals, may have been brought about by the retention 

 of the second polar body, or by a premature division of the chro- 

 mosomes without the division of the cell body just before the first 

 cleavage. It is hoped in the near future to determine how this con- 

 dition has arisen. 



At the present time the mechanism producing the two sexes in 

 both the normal and parthenogenetic frogs is undetermined. Levy^ 

 in Rana esculenia, and Swingle^ in Rana pipiens, describe a sex chro- 

 mosome in the normal male. But the evidence of neither of these 

 authors is convincing. There are some interesting theoretical possi- 

 bihties by which a predominance of parthenogenetic males over 

 females, as indicated by the numbers so far obtained, might be pro- 

 duced, and it is hoped that further observations will reveal the exact 

 mechanism. 



2 Levy, F., Arch. Mikr. Anat., 2te AM., 1915, Ixxxvi, 85. 



3 Swingle, W. W., Biol. Bull., 1917, xxxiii, 70. 



