Mr Doncaster, On the Inheritance of Coat-colour in Rats. 217 



recessive forms (3 and 5) than with the dominants (1, 2, 6, 7). 

 Albinos bred together gave only albinos. Two points of consider- 

 able interest are mentioned with regard to the self-coloured 

 varieties 1 and 7 ; they are left unexplained, but it seems probable 

 that they are connected and depend upon the same causes. The 

 first of these is that the self-coloured varieties when bred together 

 can give the forms with white marks, but not the pied forms, but 

 that the varieties with white marks bred together may give all 

 the types; that is to say, that type 7 for example can contain 

 type 6, and type 6 can contain both 5 and 7, but that 7 cannot 

 contain 5. This as it stands appears inexplicable, but there are 

 indications of a possible explanation. Type 6 (black with some 

 white below) has two sub-varieties, one with very little white, the 

 other with a large patch, and my work shows that the first of 

 these is closely related to the self-black (type 7), while the second 

 is a heterozygous form always containing type 5 (piebald). The 

 second point of interest arising from Crampe's work is that two 

 kinds of first crosses appear when the wild rat is bred with the 

 albino, one of which has no white (type 1), the other with white 

 below (type 2). These two varieties behave differently as regards 

 their offspring in the same way as types 6 and 7, and the expla- 

 nation appears to be that some albinos carry the self- character, 

 giving first cross of type 1, others the piebald character, giving 

 type 2. 



The animals with which I began my experiments were ob- 

 tained from several sources, but the majority were sent me by 

 Miss Douglas, of Worcester, to whom I am also indebted for much 

 useful information. I wished to cross the wild M. decumanus 

 with the different colour varieties, but failed to get wild animals 

 ■to. ■ breed in captivity. I was fortunate, however, in obtaining 

 from a local ratcatcher two families of young rats from albino 

 does by wild bucks. The man keeps a large cage of white rats, 

 from which two does escaped, and not long afterwards both rats 

 were found in nests in a neighbouring haystack with families of 

 exclusively brown young. I saw them when still with the mothers, 

 and as there are numerous wild rats about the place, I think 

 there can be no doubt that their male parents were common 

 wild rats. 



My earlier experiments were somewhat indiscriminate in 

 character, being undertaken partly to test whether the animals 

 used were pure or were giving gametes of more than one kind, 

 partly to determine the proportion in which the different forms 

 appeared among the descendants of the wild rat crossed with 

 albino. Gradually, however, definite problems presented them- 

 selves, and my later work has dealt chiefly (a) with the power 

 of albinos to transmit colour or pattern when mated with coloured 



