54 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



ings which produced offspring of that character, and a deficiency, 

 almost as great, of albinos. If these deviations from the expected pro- 

 portions indicate anything other than a chance result, it is an increase in 

 the proportion of gametes bearing the character pink-eye associated 

 with pigmented coat, and a corresponding diminution in the propor- 

 tion of albino gametes. Yet such a change is of very doubtful occur- 

 rence ; more probably the outcome is a chance one, for the deficiency 

 of albinos produced by the eight pairs which had pink-eyed young is 

 more than offset by an excess of albinos produced by the other thirteen 

 pairs, the total young produced being 121 pigmented to 30 albinos. 



The fact, too, that certain pairs of this category produced no albinos 

 must not be taken as conclusive evidence that the animals mated did 

 not contain recessive albinism. The expectation is that only i in 4 of 

 the young produced will be albinos, and it is not surprising that, as a 

 chance result, no albinos should be found among as few as the 3 to 9 

 young produced by a pair. More extensive tests, or the simpler test 

 of mating with albinos, would without doubt have shown the forma- 

 tion of albino gametes by each of the parents in question, if they really 

 were of the parentage indicated in Darbishire's table. 



The foregoing considerations indicate that the correctness of the 

 classification of pairs in the cases previously examined is not estab- 

 lished beyond question. For example, a pair which in a total of 6 or 

 8 young has produced only those of two sorts, might in subsequent lit- 

 ters produce young of the third sort, which would place the parents in 

 a different category. Only in the cases where young of all three sorts 

 have been produced is the character of a pair conclusively estab- 

 lished. In other cases the probability of correctness in the classifica- 

 tion made increases with the number of young produced. Whatever 

 errors are involved tend to increase the magnitude of Group IV (pp. 

 50 and 52) at the expense of Groups I to III, and that of II and III at 

 the expense of I. Making all allowance for such possible errors, there 

 would still seem to be little reason to question the existence, among 

 Darbishire's dark-eyed mice of generation F 2 , of all the four classes 

 designated (i) to (4) on page 48. 



The existence of the two classes of pink-eyed pigmented mice (5) 

 and (6), page 48, is strongly indicated by matings inter se of pink- 

 eyed mice belonging to generation F 2 , as recorded by Darbishire in his 

 Table H, page 37. According to our hypothesis, the pink-eyed mice 

 of this generation are in character either P p or P p (A p), individuals 

 of the latter sort being twice as numerous as those of the former. Not 

 any of them contain the dark-eyed character ; consequently they should 

 produce only pink-eyed young or albinos, when bred inter se. The 



