366 EXPERIMENTAL STUDY OF INHERITANCE 



shell cats are very rare. In this case, the results are compUcated 

 by some peculiarity wrapped up with " sex." 



When a male tortoiseshell is paired with a female tortoiseshell 

 the kittens are tortoiseshell, orange, and black — ^which is what 

 Mendehan theory would lead us to expect. 



Horses. — In horse-breeding we have usually to deal with a 

 highly prepotent sire, and there seem to be no reliable facts illus- 

 trating Mendelian inheritance. It is known, for instance, that 

 bay and brown colours are dominant in relation to chestnut, but 

 this fact is not enough in itself to warrant us in inferring that 

 Mendehan phenomena occur. It has been said by some breeders 

 that in the mating of Clydesdales and Shires there are some- 

 times Mendelian phenomena. 



Sheep. — From statistics published by Graham Bell, illustra- 

 tions of Mendelian phenomena have been inferred by Davenport. 

 Thus, three white sheep, with exclusively white ancestry (so far 

 as known), were crossed with black sheep, and the 13 lambs were 

 aU white. When hybrids of this origin were paired with black 

 sheep, there were 26 white lambs and 25 black lambs — in 

 accordance with the Mendelian expectation. When the hybrid 

 whites were inbred they produced 40 white lambs and 7 black 

 lambs (instead of the theoretical 11 or 12). But the numbers in 

 these cases are far too small to be satisfactory. 



When half-bred sheep, resulting from Border Leicester rams 

 and Cheviot ewes, are inbred, they breed true to their own type, 

 which is a distinctly non-MendeHan phenomenon. 



Man. — ^There is as yet no secure evidence of Mendelian 

 phenomena in man, but there has not been time for much 

 investigation. Attempts have been made to find evidence in cases 

 of albinism among negroes (Castle) and the lineage of families 

 inclined to polydactyhsm, but the cases are very inconclusive.* 



* Castle's case is reported in Science, xvii., 1903, but we have not seen 

 the paper. An albino in a negro family had offspring by a negro, the 

 children were negroes, but in the next generation there was a splitting 

 into negro and albino types. 



