22 ORIGIN OF A POLYDACTYLOUS RACE OF GUINEA-PIGS. 



6. PROGENY OF THE FIFTH POLYDACTYLOUS GENERATION. 

 Only one male, ^3046 (tables I and 15), in this generation, has been 

 extensively tested, and he has been used almost exclusively in matings with 

 the best four-toed stock. His young in that sort of mating grade very 

 high, viz 97, the standard of perfection being 100. He was mated to a 

 female of class N' a single time, and produced three normal offspring and 

 one polydactylous ; these three were the only normal young he ever got in 

 a total of ninety- two young. But this same mother bore to J* 1263 a litter 

 of four young, all polydactylous. Facts like this indicate characteristic 

 potencies on the part of gametes furnished by certain individuals, these 

 potencies perhaps being handed on from generation to generation, as from 

 $ 628 to his son, $ 1003. 



7. INDIVIDUAL POTENCY VERSUS ANCESTRY. 



The factor of gametic potency is evidently much greater than that of 

 ancestry. For if we arrange the various sires in the order of the respective 

 amounts of polydactylous ancestry which they possess (table 15), we see 

 at once that this is not the order of their potencies, for those having the 

 same amount of polydactylous ancestry often differ much in the potency with 

 which they transmit the polydactyl character. 



8. EXTRA-TOE OF LEFT SIDE BEST DEVELOPED. 



The extra-toe, in the case of <$ 23, was found on the left side of the 

 body only. Among his descendants, also, the extra-toe, if present on one 

 side of the body only, is more apt to be found on the left side. When the 

 extra-toe is found on both sides of the body, but unequally developed, it is 

 oftener the left side which has the better developed toe. The difference is 

 not great, but is quite constant. Thus there have been recorded the follow- 

 ing numbers of polydactylous feet : Left, 630 ; right, 589. These totals are 

 made up from various partial sums given by different generations or families 

 as follows: 



Total. 



Left 61 66 51 41 18 98 112 21 51 34 24 53 630 

 Right 56 65 50 39 15 86 in 20 50 32 20 45 589 



In every case the left toes slightly outnumber the right ones. 



The extra-toes, as regards both degree of development and position on 

 the body, are distributed as shown in table 16. 



The extra-toe, it will be observed, occurs oftenest on the left side of 

 the body, particularly in its higher grades of development (G and F). 



