Nos. 620-621] INHERITANCE IN PEBOMYSCUS 



445 



I am now able to indicate rather more definitely the mode 

 of transmission of this character. I wish to lay some 

 stress here upon its genetic behavior, since I regard it as 

 an interesting case in its bearings upon certain theoretical 

 questions. 



The pale-nosed condition has been studied only in the 

 darkest of my races, rubidus. It was not noticed in the 

 original wild stock, but it may well have been overlooked, 

 as it is not a conspicuous character, and I was not search- 

 ing for this type of variations when the wild generation 

 was examined. In the first cage-born ("Cj") generation 

 twelve mice were recorded as having white-tipped snouts, 

 four of the cases being entered as doubtful. At the time 

 of examining these animals I had no idea as to the par- 

 entage of the individuals, so that there was no bias in my 

 selection. Upon looking up their pedigrees, I found that 

 ten of the twelve cases (eight certain and two doubtful) 

 were the offspring (indeed, the only offspring) of two 

 mothers of the wild generation (P ? 40 and 41) by a single 

 father (P J 15). The other two cases (both doubtful) 

 were of other parentage. In connection with the figures 

 just given, it must be stated that the C t generation con- 

 sisted altogether of 60 (surviving) individuals, these 

 being the progeny of twelve females and nine males. 



Only 38 mice were obtained in the G 2 generation, 6 of 

 which had white-tipped snouts. As before, the count was 

 made without my being aware of the parentage of the 

 individuals examined. Of the six " mutants,' * it turned 

 out that four belonged to a fraternity of five, the fifth 

 member of which was normal. This fraternity was the 

 offspring of 2 61 (normal) by C, <$ 10 (white-nosed). 

 The other two mutants were the offspring of this same 

 G 1 2 61, by one of her brothers (J 3), the latter being like- 

 wise normally pigmented. These parent animals we may 

 believe to have been heterozygous. 



Unfortunately, none of the matings of the pale-nosed Cj 

 individuals inter se proved fertile, and indeed the only 

 one of these aberrant mice which left descendants was 

 the <$ 10 referred to above. 



The relationships here indicated, and the incidence of 



