THE CHROMOSOMES OF PARTHENOGENETIC FROGS AND TADPOLES.
1. This paper presents cytological observations upon Dr. Loeb's parthenogenetic frog material, with considerations upon the mechanism by which the diploid number and both sexes may be produced. 2. Both sexes of adults and tadpoles are present. 3. The chromosome number is diploid and probably 26 in both sexes. Sex chromosomes cannot be distinguished. 4. The chromosome numbers observed by other authors in parthenogenetic frog material are haploid, diploid, and variable. Their significance is considered. 5. The mechanism producing the diploid number, based on European observations, appears to be a doubling of the haploid number at some time after the second polar body is given off. 6. Overripeness may be a factor in producing both sexes of parthenogenetic frogs and tadpoles. 7. Genetic data indicate that the normal male is digametic and that there are differences of potency between male and female factors for sex which vary in frogs of the two races and in strains within the race. These differences have been interpreted by Witschi as forming a series of multiple allelomorphs.
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Zoological Laboratory of the University of Pennsylvania, Philadelphia.