ON THE LEFT-SIDED INCIDENCE OF THE SUPER- 

 NUMERARY DIGIT IN HETERODACTYLOUS FOWLS. 



By C. J. BOND, C.M.G., F.RC.S. 



The following results have been obtained by crossing representatives 

 of certain five-toed with four-toed breeds of Fowls. 



The breeds chosen were the Silky, Dorking and Faverolle on the one 

 hand and the Old English Game, Wyandotte and Orpington on the 

 other. The proportion of four-toed to five-toed and heterodactylous 

 offspring (birds with five toes on one foot and four on the other) varied 

 somewhat according as the male or female parent belonged to the five- 

 toed breed and also in the F^ as compared with the F2 generation. 



Out of a total however of 402 birds 172 developed four toes on both 

 legs, 192 five toes on both legs and 38 were heterodactylous. 



Of these heterodactylous birds 34 had the extra digit on the left 

 side and only 4 on the right side. 



The proportion between the numbers of four-toed, five-toed, and 

 heterodactylous birds in the different matings and in the two generations 

 is shown in the following- table : 



Totals 172 192 38 



The tendency of the Eodra Digit to appear on the Left Side in the 

 Asymmetrical Birds. 



In the early matings the supernumerary digit appeared on the left side 

 in all the asymmetrical birds and it was only on mating a heterodactylous 

 cock with heterodactylous hens of the F^ generation that the extra 



