94 HEREDITY AND EUGENICS 



development by the presence of other determiners. 

 Many instances of the influence of hereditary de- 

 terminers upon each other are now known from 

 experimental breeding. 



Schofield (1922) describes a case of webbed toes 

 which occurs in fourteen male members of a family 

 in four generations. The web appears only between 

 the two toes next the great toe, and is confined to the 

 skin and flesh. It is always more marked in the 

 right foot than the left, and is confined to the males, 

 being transmitted only from father to son. It thus 

 follows the course of the Y-chromosome. The only 

 case of this type of inheritance which has been 

 experimentally investigated (Schmidt, 1920) occurs 

 in the " millions " fish, Lebistes reticulatus, which is 

 a native of the West Indies. A dark spot on the 

 dorsal fin in certain males is transmitted in crosses 

 to all the male offspring, but is not transmitted 

 through the female line at all. Castle (1922) has also 

 recently pointed out the significance of this type of 

 inheritance in man. 



Polydactyly and syndactyly in various forms are 

 not infrequently found together. A case of the kind 

 has been described in cats (Howe, 1902). A strain of 

 polydactylous cats in Cambridge, Massachusetts, was 

 descended from a polydactyl cat at the Harvard 

 Astronomical Observatory. One of these cats was 

 dissected, having six toes on each fore paw, and the 

 toes of the hind paws fused in pairs almost to the ends 

 of the claws. 



Castle (1906) has described the origin of a poly- 

 dactylous race of guinea-pigs. He sa3^s that in man 

 " polydactylism usually makes its (recorded) ap- 

 pearance in some noteworthy form, is transmitted 

 more or less strongly through tw^o to five generations, 

 and then disappears, doubtless so weakened by re- 

 peated outcrosses that its manifestations, if any occur, 



