ISO S. W. GEISER. 



(one male to three or seven females) are suggestive of this 

 explanation of the atypical adult ratio. 



The special chromosomes whose presence or absence appears 

 in many animals to be associated with a definite sex have not 

 yet been reported s on cytological grounds for any teleost fish. 

 If we knew that such a chromosome (or chromosomes) existed 

 in the sex-cells of a given species, thus giving rise to dimorphic 

 zygotes on fertilization, we could forecast approximately equal 

 numbers of the sexes at birth (secondary sex-ratio of Schultz, 

 '18), unless the gametes showed a differential viability. This 

 cytological method of ascertaining primary and secondary sex- 

 ratios is of course the most dependable one we have. Failing 

 in this, valid conclusions may also be reached by taking large 

 litters and raising them with as few mortalities as possible to a 

 stage where the sexes may be distinguished. Unless the early 

 sex-ratios are ascertained by one of these methods, the results 

 are quite untrustworthy. Apparently only three workers, Eigen- 

 mann ('96), Punnett ('04), and Hubbs ('21) have done this. 

 The first mentioned, in his work on the viviparous Embiotocid 

 Cymatogaster ascertained the sex-ratio of litters before birth by 

 microscopical examination of the embryo-gonads, and found the 

 sexes approximately equal in numbers in the litters. Punnett 

 ('04) in a similar way found the sex-ratio in the Elasmobranch 

 Spina.v to be approximately a 1:1 ratio, and Hubbs ('21) ob- 

 tained results similar to those of Eigemnann in the Embiotocid 

 teleost, Amphigonopterus. Only the sex-ratios of adults can be 

 learned by external observation of the individuals of a popula- 

 tion. It is certain, of course, that if no differential death-rate 

 of the sexes exists in a given species, the sex-ratios of adults will 

 give a trustworthy index to the sex-ratios at fertilization and 

 at birth, as appears to be the case in the lake whitefish, Coregonus 

 albus, as reported by Pearl ('16). 



As has been saidf in Gambusia the females are greatly in ex- 

 cess of the males. The following cytological and experimental 

 studies were undertaken with the view of ascertaining whether 



2 No differences have been found between the sex chromosomes and the 

 autosomes in the poeciliid teleost, Lebistes. (Winge, '220, also in C. R. Lab. 

 Carlsberg, Vol. 14, No. 17, p. 8, 1922.) 



