IS THE FERTILE TOKTOISE-SHELL TOM CAT 

 A MODIFIED FEMALE ? 



By C. C. little. 



Carnegie Institution of Washington, Cold Spring Harbor, L. I., 



New York. 



Doncaster's recent suggestion^ that the tortoise-shell torn cat might 

 be the result of the process of hormone action during embryonic life, 

 analogous to that producing free martins in cattle, is an interesting one. 

 The whole question of tortoise-shell tom cats . has been so frequently 

 discussed, that it is certainly to be hoped that someone with adequate 

 facilities will shortly put this last suggestion to an experimental test. 

 Inasmuch, however, as any breeding work with cats involves considerable 

 time and expense, it seems desirable to point out certain fundamental 

 difficulties which Doncaster's hypothesis meets with at the outset. 

 Sterility in tortoise-shell tom cats, which appears to be the rule when 

 such animals are found, is equally explicable on the hypothesis of " non- 

 disjunction" advanced by the writer and on that of hormone action 

 advanced by Doncaster. 



Both hypotheses predicate the formation of sterile males of colours 

 other than tortoise-shell, which would, because of their similar somatic 

 appearance to ordinary fertile males, be easily overlooked. Where there 

 is presumably an XX condition of the sex chromosome in the female, 

 non-disjunction is theoretically possible, and similarly where there are 

 embryos in close juxtaposition within the same horn of the uterus, free 

 martinism is theoretically possible. So far then as the sterile male forms 

 are concerned, both hypotheses have a certain basis for acceptance in 

 observed experimental fact. 



The real difficulty comes when a fertile tortoise-shell tom cat is 

 encountered. In this case the hypothesis of non-disjunction is able to 

 account for the observed facts, provided peculiar somatic behaviour of a 

 pair of colour characters already showing an unusual type of coat pattern 



' Journal of Genetics, Vols. viii. and vs.. 



