L. DONCASTER 337 



occasionally a tortoiseshell female embryo would be masculized. It 

 must be assumed that the masculization is more complete in the Cat 

 than in Cattle, so that the testes, instead of only comparatively rarely 

 descending into the inguinal canal, regularly reach the scrotum, and the 

 external genitalia also assume the male type. Since, however, Magnusson 

 finds a series of stages between an almost female and a nearly male 

 condition, it is not a very improbable assumption that in the cat the pro- 

 cess is habitually carried further. Possibly the fertile tortoiseshell male, 

 which on the evidence of Sir Claud Alexander (quoted by Cutler and 

 Doncaster) must be admitted to exist, is the final stage of the series. 

 Complete conversion into males of embryos which are genetically 

 female appears to exist in some of Goldschmidt's Lymantria crosses (3) 

 and in several hybrids between different species of moths. 



This hypothesis involves the assumption that females of colours 

 other than tortoiseshell must also at times be changed into apparent 

 males, but since these would naturally be regarded as males which for 

 some reason or other were not successful breeders, no record of them 

 would be preserved. The suggestion here put forward does not seem 

 difficult to test. By collecting gravid uteri of cats and examining the 

 foetal membranes it should not be difficult to find out whether confluence 

 between the blood-systems of neighbouring foetuses ever takes place. 

 If it did, and if one of the foetuses was definitely male, then according 

 to the hypothesis the other foetus should, in two cases out of three, have 

 testis-like gonads with no seminal cells in the tubules. 



The writer does not feel confident of being able to carry out the 

 considerable labour involved in testing the hypothesis in the immediate 

 future, and he puts it forward in the hope that some other may be able 

 to obtain and examine the necessary material. 



PAPERS REFERRED TO. 



Chapin, Catharine L. " A microscopic study of the reproductive system of 



foetal free-martins." Jownx. Exp. Zool. Vol. xxiii. 1917, p. 453. 



Cutler, D. W. and Doncaster, L. " The Sterility of the Tortoiseshell Tom-cat." 



Journal of Genetics, Vol. v. 1915, p. 65. 

 GoLDSCHMiDT, R. " Experimental Intersexuality and the Sex Problem." Amer. 



Nat. Vol. L. 1916, p. 705. 

 LiLLiE, F. R. " The Free-martin : a study of the action of sex-hormones in the 



foetal life of cattle." Joum. Exp. Zool. Vol. xxni. 1917, p. 371. 



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