VoLUilli V 



DECEMBER, 1915 



No. 2 



ON THE STERILITY OF THE TORTOISE- 

 SHELL TOM CAT. 



By D. W. cutler, B.A., 



Scholar of Queens College, Cambridge ; 



AND L. DONC ASTER, F.R.S., 

 Fellow of Kiug'ti College, Cambridge. 



In a note by one of us in the Proceedings of the Cambridge 

 Philosophical Society, Vol. xvii. 1912-14, p. 307, entitled "A possible 

 connexion between abnormal sex limited transmission and sterility," 

 it was suggested that tortoiseshell torn cats are usually sterile. In an 

 earlier paper' evidence was given that the rare tortoiseshell male cat 

 might be produced b}' the failure of the normal sex-limited transmission 

 of the yellow factor from the male parent. When a yellow (orange) 

 male cat is mated with a black female, the normal result is that all the 

 female offspring are tortoiseshell, all the males black, showing that the 

 yellow factor is sex-limited in its transmission by the male, and goes 

 only into the gametes which will give rise to females. There is some 

 evidence, however, which seems to point to the conclusion that tortoise- 

 shell males may be pi'oduced by a yellow male parent mated to a black 

 female; this is apparently brought about by the failure of the yellow 

 factor always to pass to female producing gametes. A male produced in 

 this manner would presumably be a tortoiseshell. A tortoiseshell male 

 has been in our possession for more than two years and we have 

 repeatedly endeavoured to mate him with a black female in order to 

 find out how the yellow and black factors are transmitted by a male cat 

 in which both arc present. Although copulation has occurred many 

 times with each of four females when on heat, apparently with success, 

 yet pregnancy has never followed with any of the females used. These 



SiJi 



,/iiurn. of (jciielics, Vol. iii. 1913, p. 11. 



Joiirn. of Gen. v 



