L. DONCASTER 15 



over unaffected males, but that this is not a constant feature, and when 

 it occurs it is improbable that it is duo to partial sex-limitation among 

 the gametes of the transmitting female. Further, it is probable, if not 

 certain, that occasional exceptions occur, suggesting that an affected 

 man may very rarely transmit the fiictor for the affection to a son, and, 

 correspondingly, may occasionally fiiil to transmit it to a daughter. 



The difficulties in the way of an elucidation for the human cases 

 arise chiefly from the impossibility of distinguishing a transmitting 

 female except by the fact that she has affected sons. In the hope of 

 throwing further light on the question, I compared my summaries of 

 human pedigrees with data which I have collected during several years 

 of colour-inheritance in Cats, and find that they are in most respects so 

 closely similar that I believe the inheritance of certain characters in the 

 Cat may provide a solution of the problems which cannot be answered 

 by means of human pedigrees. In the case of the Cat the " trans- 

 mitting female " is visibly different from the non-transmitting, and the 

 most serious source of eiTor affecting the human data is thus avoided. 



The character in the Cat which appears to correspond in its 

 inheritance with the sex-limited affections in Man is the orange colour 

 as contrasted with the black which corresponds with " normality." In 

 1904', in a short note on the subject, I concluded that in the Cat the 

 orange colour is dominant over black in the male, but only partially 

 dominant in the female, so that the female heterozygote is tortoiseshell. 

 The existence of sex-limited inheritance was at that time scarcely 

 known, but I mentioned the fact that among my collection of data 

 there was no case of an orange male mated with a black female giving 

 orange male kittens ; the females from such a mating were tortoiseshell, 

 the males black. Subsequent collection of further data has shown con- 

 clusively that the transmission of the orange colour by the male is 

 sex-limited, and the same result has been arrived at independently by 

 C. C. Little from his own experiments-. 



In general, the results obtained with Cats are as follows : — an orange 

 male mated to a black female gives black male and tortoiseshell female 

 kittens ; in the converse cross, orange female by black male, the male 

 kittens are orange, the females tortoiseshell. The orange male thus 

 usually transmits orange to his daughters only, the orange female 

 transmits it to all her offspring of both sexes. A tortoiseshell female 

 by black male gives orange and black males, tortoiseshell and black 



1 Proc. Camb. Phil. Soc. Vol. xiii. p. 35. 



2 Scierice, May 17, 1912. 



