l6 COAT CHARACTERS IN GUINEA-PIGS AXD RABBITS. 



family of guinea-pigs. The animals enumerated were all pigmented; 

 those marked (/'), when mated with albinos, produced only pigmented 

 young showing that they were pure ; the others produced some albino 

 offspring, when mated with albinos (or with other hybrid pigmented 

 animals), showing themselves to be hybrid in character. In the case 

 of one animal only (9 207) no test was made as to the production of 

 albino gametes. This animal was paired with pure pigmented mates 

 only, and the young were, of course, invariably pigmented. 



It will be observed from fig. 9 that pure 9 7 was mated with two 

 different hybrid males, viz, cf R and c? A. By cT R she had four 

 daughters (9 7.1% $ 7.1% 9 7.1% and 9 7.1*), two of them pure (P), 

 two hybrid in character. By c? A she had two daughters (9 7.3" 

 and 9 7-3'') , both hybrid in character. In the next generation, hybrid 

 cf A was mated with pure 9 7- lC ' producing in three different litters 

 seven pigmented young, which were used as breeders. One of these 

 (9 207) was not tested for recessive albinism, as already stated. Of the 

 others, four proved to be pure, two hybrid in character. Altogether 

 there were among the young indicated in the table six pure individuals, 

 six hybrids, and one of uncertain character. 



So far as observed, there are no intermediate conditions between pure 

 and hybrid pigmented animals. If an animal forms albino gametes at 

 all, half its gametes are of that character. Of course in individual 

 litters, or when only small numbers of offspring are dealt with, con- 

 siderable deviations from the Mendelian ratios are likely to be encoun- 

 tered. This is to be expected on the theory of probabilities, as Allen 

 ( : 04, p. 1 10) has clearly pointed out. But when more extensive tests 

 are made the expected ratios are more closely approximated. 



ALBINISM AND THE "LAW OF ANCESTRAL HEREDITY." 



The foregoing results show very clearly that albinism conforms 

 in its mode of inheritance to Mendel's law of heredity. The fact, 

 however, must not be overlooked that a somewhat different explanation 

 of its inheritance has recently been given, based on Gallon's " law of 

 ancestral heredity." I shall not at this time enter into a detailed dis- 

 cussion of Gallon's hypothesis, which was an entirely rational one in the 

 form in which it was originally proposed, and quite in harmony with the 

 phenomena of gametogenesis as then interpreted. I have shown else- 

 where (Castle, :O3'') by a specific test in the case of mice, based on the 

 observations of Von Guaita ('98, :oo), that Gallon's law fails to account 

 for the observed facts concerning the inheritance of albinism, but that 

 Mendel's law does this perfectly. Nevertheless Darbishire ( : 04), like- 

 wise dealing with albinism in mice, though admitting that certain of 

 his results are not in disagreement with Mendel's law, is inclined rather 



