THE CHROMOSOMES OF PARTHENO GENETIC FROGS. 



BY CHARLES L. PARMENTER. 



(From the Zoological Laboratory of the University of Pennsylvania, Philadelphia.) 



(Received for publication, December 1, 1919.) 



Among the important features of interest in connection with par- 

 thenogenetic frogs are the chromosome number and the sex-deter- 

 mining mechanism. At the suggestion of Doctor Loeb, I have 

 undertaken the investigation of these problems by using some of 

 the parthenogenetic frogs and tadpoles which he has thus far raised. 



Previous to 1919, Doctor Loeb had succeeded in raising twenty- 

 frogs to the adult condition.^ Fifteen of these were males, three were 

 females, and the sex of the remaining two was undetermined. In 

 1919, he succeeded in raising 65 tadpoles to metamorphosis. One of 

 these has metamorphosed, seventeen have been fixed for cytological 

 purposes, five have died, and the rest are still tadpoles. 



The chromosomes of the gonads of one of these adult males and of 

 thirteen of the tadpoles have been examined. In all these individuals 

 the number is clearly diploid. The only two spermatogonial com- 

 plexes of the adult male, sufficiently clear for study, show about 

 twenty chromosomes distinctly and others superimposed, as pre- 

 viously stated.^ Among the cells undergoing maturation are tetrads 

 in the late prophase stage. These tetrads appear as rings, either 

 completely closed or slightly open at one point. They are appar- 

 ently of the same form as tetrads of the normal material. Their 

 number is clearly haploid, but an exact count has not yet been 

 obtained. In the sections of the gonads of the thirteen tadpoles there 

 are many complexes in which all but one or two chromosomes are 

 entirely clear, and several mitoses in which all the chromosomes are 

 well separated but cannot be counted with certainty because the cell 

 has been cut in sectioning. However, the number of chromosomes 

 in a limited number of complexes of two individuals is definitely 

 twenty-six. 



. 1 Loeb, J., Proc. Nat. Acad. Sc, 1918, iv, 60. 



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