MENDEL'S LAWS OF HEREDITY 251 



Guinea-pigs. — If a black guinea-pig of pure race be crossed with 

 a white one the offspring will be all black , and if these are mated with 

 each other the recessive white character reappears on the average in 

 one in four of their offspring. These whites mated with each other 

 produce only white offspring, while the black are as usual of two kinds, 

 pure blacks and impure blacks. Similarly, as Professor Castle has 

 shown, a rough coat is dominant over a smooth coat, and a short coat 

 over a long coat. 



Rabbits. — Hurst paired white Angora rabbits (with pink eyes and 

 silky hair) with "Belgian hare" rabbits (with pigmented skin, dark 

 eyes, and short yellow fur). The hybrids were pigmented like the 

 " Belgian hares," but the fur was grey like that of the wild rabbit. 

 These hybrids were inbred, and 14 distinct types resulted — an apparent 

 "epidemic of variation" to which Mendel's theory has supplied the 

 clue, for four pairs of contrasted characters are involved in the hybrid 

 inbreeding — namely, short hair versus long hair, pigmented coat versus 

 albinos, grey versus black coat, uniform versus marked coat (Dutch 

 marking latent in the albinos), and the 14 distinct types illustrate the 

 possible combinations. 



As regards short hair versus long hair, Hurst found that when the 

 short-coated hybrids were inbred they produced short-haired forms 

 like the Belgian hare grandparent, and long-haired forms like the 

 Angora grandparent. Out of 70 which reached the age of two months 

 or more, 53 were short-haired and 17 long-haired — a close approxi- 

 mation to the Mendelian anticipation, 52.5 : 17.5. Similarly, as 

 regards pigmented coat versus albino, the hybrids, when inbred, 

 yielded 132 pigmented and 39 albino forms — a close approximation to 

 the Mendelian expectation, 129 : 43; and so on. 



Cats. — There are some interesting results as to colour (Doncaster). 

 Thus, " pure" orange ? crossed by " pure " black $ gives tortoiseshell 

 females and yellow males, but black crossed by orange gives black 

 males or females, tortoiseshell females, and orange males. It seems 

 that orange usually dominates over black in males, while in females 

 the orange (for some unknown reason) is less dominant and tortoise- 

 shell results. Male tortoiseshell cats are very rare. In this case the 

 results are complicated 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 Mendelian 

 theory would lead us to expect. 



Man. — Evidence of Mendelian phenomena in man is as yet very 

 scanty. It appears that the condition known as brachydactylism. 



