species crosses in Rats. 1I5 



between colour and albinism aud that these genes were different, one 

 being in this respect NNmm and the other nnMM. This is a case, 

 which is similar to that discovered by Bateso n in the Sweet pea, where 

 two whiteflowered strains of Emily Henderson differed in genotype, 

 and each possessed a gene lacking in the other. In Bateson's case, 

 and in his similar case in poultry, the coloured hybrids gave coloured 

 and white descendants in a 9 : 7 proportion. We were anxious to see 

 the result of our matings of coloured young from two albino parents. 

 Only two pairs could be raised to maturity. 



On pair produced 15 agoutis and 8 albinos, and the other pair 

 gave 7 agoutis and 8 albinos. If we add the results, we get 22 agoutis 

 and 16 albinos, which is fairly close to a 9 : 7 ratio. It will remain 

 to be seen whether it will be possible to breed the two kind of albinos, 

 those lacking N and those without M. There seems to be a slight 

 variability in tinge among our albinos. 



We saw that in the F2 generation, two waltzing fieldrats appeared. 

 It has been found impossible to propagate these rats. The waltzing 

 fieldrats are less helpless than the houserat waltzers, and they are not 

 deaf. But the tw'o females that ever bred in our cages, never took any 

 interest in the young. In the origin of the novel character, we again 

 meet with the fact that it appeared in a proportion suggesting one in 

 sixteen rather than one in four. Whether the two genes, whose 

 simultaneous absence seems to be responsible for the character, are the 

 same genes (■» and H as in the other series, is impossible to decide. 

 In fact, the mattei- seems to have been still more complicated. For 

 when we did succeed in obtaining a full litter of seven diving young, 

 from two waltzing parents, these seven young rats were all normal. 

 This litter was raised by a fostermother in the ratcolon}' of the 

 Department of Anatomy of this University. 



In the series of processes which ultimately lead to the pigmentation 

 and distribution of pigment seen in wild rats, a great many develop- 

 mental factors play a rOle. Absence of one or more of the genes 

 involved may either result in a different, recessive colour, yellow, or 

 chocolate or cream, but it may also result in albinism. Any link of 

 any importance in the chain of factors necessary for pigmentation may 

 be indispensable for pigmentation. This means that absence of this 

 gene would produce albinism. In a wild species of rats the number of 

 such indispensable links may well be high, so that absence of either 

 X, Y or Z would result in albinism. On the other hand it is not 



8* 



