PHYSICAL CHARACTERS IN MAN 95 



are no longer observed." Normal guinea-pigs have 

 four toes on each front foot, but only three on each 

 hind foot. Castle's polydactylous race had four on 

 all feet. The missing digits in normals are the thumb 

 from the fore feet, and I and V from the hind feet. 

 The polydact\dous race was established from one rare 

 individual (mutation), and was afterwards found 

 twice in breeders' animals, but was not hitherto 

 known in any wild or domesticated Caviidce. By 

 selection through five generations a polydactylous 

 race was gradually established in which all the 

 offspring were polydactylous. The inheritance is 

 neither Mendelian nor blending, but probably inter- 

 mediate between the two. Without the aid of 

 selection, polydactylism would probabl}^ never become 

 a racial character. 



In poultry, Bateson, Davenport, and others have 

 shown that the extra toe, which has for a long time 

 been an established character in some breeds, is not 

 strictly Mendelian in its inheritance, although it is 

 more strongly established than in the four-toed race 

 of guinea-pigs. 



Radiograms of a hexadactylous Italian immigrant 

 with six fingers and toes are given in Joiirn. Heredity, 

 vii., 320 (1916). The condition appears to be due to 

 a split in the rudiment of the fifth finger. A five- 

 toed pigeon, due to a similar split in the rudiment of 

 one toe, is also shown. A case in which the thumb 

 is more or less completely missing from both hands 

 is photographed in Journ. Heredity, vii., 224 (191 6). 

 There were various digital malformations in the 

 relatives. 



Bond (1920) crossed various five-toed and four- 

 toed breeds of fowls. The former were the silky 

 Dorking and Faverolle, and the latter Old English 

 Game, Wyandotte, and Orpington. The proportions 

 of four-toed to five-toed and heterodactylous birds 



