COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 1C) 



Instead of producing less than 25 per cent of albinos, as Darbishire 

 supposes them to do, matings (2) and (3) really produce more than 

 that proportion of albinos. Considered separately they produce, one 

 somewhat more than 25 per cent, the other somewhat less, as we 

 should expect to be the chance result where small numbers of young 

 are considered. 



In further evidence that Darbishire's " extracted hybrids" did not in 

 all cases contain recessive albinism, his matings of such animals with 

 albinos are instructive (see his Table F, p. 36). Five out of nineteen 

 such matings failed to produce any albinos whatever, though they pro- 

 duced a total of 19 young, all pigmented. If the pigmented parents in 

 these matings had really been hybrids, half their young should have been 

 albinos. Such was precisely the proportion of albinos produced by the 

 fourteen matings in which the pigmented parent, though of the same 

 ancestry as in the foregoing cases, showed itself to be really a hybrid, 

 for these fourteen matings produced 36 pigmented young and 36 albinos. 



Darbishire designates the cases just discussed " the most conclusive 

 results which I have obtained " [in favor of the law of ancestral hered- 

 ity]. Careful examination of these results, however, as we have seen, 

 makes them seem far from conclusive in favor of that hypothesis. I 

 have, therefore, thought it worth while to apply a further experimental 

 test to Darbishire's hypothesis, in the case of guinea-pigs. 



In doing so I class as a hybrid pigmented animal (i) any pigmented 

 animal known to have had an albino parent, or (2) any pigmented 

 animal born of pigmented parents which has produced one or more 

 albino young. In Tables A and B are summarized the results of all of 

 the matings between two animals known to be hybrids, or between a 

 hybrid and an albino, which have been made in my later experi- 

 ments. Matings from my earlier experiments are not included for 

 the reason that the ancestry of the animals at that time used is 

 too imperfectly known. The Mendelian expectation is, as Darbishire 

 states, that all hybrids alike, whether they have few or many albino 

 ancestors, will form gametes approximately half of which bear the 

 albino character, half the pigmented character. Darbishire's con- 

 tention, on the other hand, based on the hypothesis of Gallon, is 

 that the more albino ancestors a hybrid animal has, the more albino 

 offspring will it produce. To test these alternative hypotheses I have 

 tabulated the matings which have been made in these experiments 

 according to the amount of albino ancestry involved in each, this amount 

 being greatest in the first part of each table. Table A includes matings 

 between two hybrids, Table B matings between a hybrid and an albino. 



