MENDELISM— GENERAL DISCUSSION 71 



modified type of short coat may breed true, and their 

 appearance has been attributed to " imperfect segrega- 

 tion." It seems unnecessary, however, to assume 

 imperfect segregation. The modification of the short 

 coat might be due to the transference of certain inde- 

 pendent modifying factors from the Angora. It ■\\as 

 found impossible to explain the modification of the 

 short coat by assuming one such factor, but this does 

 not prove that the modification was not due to inherit- 

 ance on MendeHan lines. 



Some of the most puzzling and irregular cases of 

 inheritance have been met Avith in fowls. We may 

 instance the case of the extra toe wliich is characteristic 

 of certain breeds. In the first place, it must be not^d 

 that the extra toe is not quite uniformally inherited 

 even in pure breeds which have long been selected for 

 this character. In the actual experiment, carried out 

 by Davenport, which we shall describe, a five-toed 

 breed was used which produced about 3 per cent, of 

 four- toed individuals. 



When this breed was crossed with a normal, four- 

 toed variety, the five-toed condition was irregular^ 

 dominant. A few birds showed five on one foot and 

 four on the other. Altogether, 27 per cent, were four- 

 toed on both feet, and the remaining 73 per cent, showed 

 five toes on either or both. Accepting, for the moment, 

 the fact of this irregularity in dominance, what result 

 should we expect in the next generation ? Twenty-five 

 per cent, ought to be like the five-toed parent breed, 

 which was about 97 per cent, five-toed. This 25 per 

 cent, ought then to be about twenty-four five-toed and 

 one four-toed ; 50 per cent, ought to be hybrids, which 

 we found to be about 73 per cent, five-toed. Our 

 50 per cent,, then, ought to be about thirty-six five-toed, 

 fourteen four-toed. Twenty-five per cent, ought to be 

 like the four- toed parent breed, all foiur-toed. On 

 adding these numbers we find the expectation to be 

 60 per cent, five-toed, 40 per cent, four-toed. Actually, 

 the percentages found were 53 and 47 respectively, 

 which, considering that the numbers were small, is 



