COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



55 



seven pairs tested by Darbishire produced 31 pink-eyed and i albino 

 young, with no dark-eyed ones conclusive evidence against the 

 " ancestry" hypothesis of Gallon and Darbishire, for all four grand- 

 parents were dark-eyed. The number of young produced by a pair 

 in this experiment ranged from 2 to 6, the single albino occurring in a 

 litter of 5. This one albino gives conclusive evidence that its parents 

 both contained recessive albinism and so were of class (5). We should 

 on the theory of probabilities expect the occurrence of three such pairs 

 in seven taken at random. It is possible that more extensive tests would 

 actually have shown the occurrence of more than this one, but it is a 

 probability which amounts almost to a certainty that not all the seven 

 pairs would have given albinos, had they been more extensively 

 tested. If not, then the occurrence of individuals of class (6), /. e., P p, 

 would be fully established by the experiment. But the absence of 

 recessive albinism from certain of the pink-eyed mice of this genera- 

 tion is shown in a simpler way, viz, by matings with albinos. Nine- 

 teen such matings are recorded by Darbishire in his Table G, page 36. 

 The number of young produced by a pair ranges from 2 to 8. Five of 

 the nineteen pairs produced albino young, showing that they contained 

 recessive albinism and transmitted it in approximately half their 

 gametes, for the young produced by these pairs are 12 pigmented to 12 

 albino. Since the remaining fourteen pairs produced not a single 

 albino in a total of 74 young, it is certain that many if not most of 

 them did not form albino gametes, for had they done so half their 

 young should have been albino. The albino parents used in this 

 test evidently all transmitted latent the black-eyed character, for every 

 one of the nineteen pairs produced dark-eyed young, showing that the 

 albino parent was either of class (8), page 48, or possibly of class (7). 

 The occurrence of an albino of this latter class (one which transmits 

 latent in half its gametes the dark-eyed character, but in the other half the 

 pink-eyed character) is shown beyond question, in Darbishire's Table 

 G, by a mating (iH 120) which produced 2 dark-eyed and i pink-eyed 

 young. The occurrence of albinos which may have been either of 

 class (7), page 48, or of class (9) (/'. <?., which transmitted the pink- 

 eyed character either in half or in all of their gametes) is indicated by 

 three pairs in Darbishire's Table F, page 36, as follows : 



