ORIGIN OF A POLYDACTYLOUS RACE OF GUINEA-PIGS. 19 



2. PROGENY OF THE ORIGINAL POLYDACTYLOUS INDIVIDUAL. 



The polydactylous male (^23), in a total of seventy-seven young, 

 produced fifteen polydactylous ones. The proportion of polydactylous 

 individuals varied much among the offspring by different mothers. (See 

 table 2.) Unrelated mothers, from families in which polydactylism had 

 not been observed, gave only two polydactylous young to thirty normal 

 ones, or 6.25 per cent, polydactylous. Related normal mothers that is, 

 mothers descended from <$ 41. i a gave nine polydactylous to twenty-seven 

 normal, or 25 per cent, polydactylous, while polydactylous mothers gave 

 four polydactylous to five normal young, or 44 per cent, polydactylous young. 



Many of the young of $ 23 had the extra digit present on both the 

 right and the left hind feet, and in several of these the digits were better 

 developed than in the father, evidently with all the appropriate muscles 

 necessary for functional toes. One of the best of these young was oT 193 

 (table i). His mother was a normal individual descended from 41. i a , but 

 gave a larger proportion of polydactylous young than any other mother had 

 done up to that time. By $ 23 she had five polydactylous and six normal 

 young. 



To express the degree of development of the extra digit a series of 

 three grades was now established, good, fair and poor, which will be abbre- 

 viated to G, F and P respectively. Good means a fully developed and func- 

 tional fourth toe; fair means a fourth toe rather smaller than the others, 

 often turned upward a little in walking, as if its muscular equipment were 

 imperfect ; poor means a loosely hanging toe, either with or without a nail ; 

 sometimes the toe described as poor is represented by only a soft fleshy bag 

 of skin attached to the side of the foot, without either nail or hair, destined 

 to shrivel up and drop off within a few days after birth. In distinction from 

 these three classes, the term normal (N) will be used to describe a three- 

 toed foot. In describing the condition of the toes of an individual, the left 

 foot will always be named first ; thus GP will mean an individual having a 

 good fourth toe on the left foot, a poor one on the right foot. 



3. PROGENY OF THE SECOND POLYDACTYLOUS GENERATION. 



Male 193, as regards the extra-toe, was classed as FF, but he pro- 

 duced about fifteen young with well-developed extra-toes, which placed 

 them in class G. About one-fourth of all his polydactylous young were of 

 this sort, the polydactylous including more than half his young (forty- 

 eight out of eighty-six). 



