]^Q4 Hagedoorn. 



yellow rats from his animals. The rats were sent to us in France, and 

 through the ignorance of some rustomhouseoffical they were sent back 

 to London, so that ultimately only five animals reached us, all agoutis. 

 Two males, which must have been Fs animals of the original cross, 

 were bred by us to French houserats, Mus rattiis. These rats were 

 from a colony taken in a farmhouse in Verrieres-le-Buisson, near Paris, 

 where all the rats were large, longtailed typical slaty black animals. 

 We obtained nine Fi animals, all black, with black belly. Thi-ee of 

 these, two females and one male grew up to maturity. 



From subsequent experiments, and from the crosses made by 

 T. H. Morgan, we know that white belly is dominant over dark belly, 

 but that the gene, whose presence in agouti rats makes the difference 

 l)etween dark and light belly, has no influence upon undercolour in 

 black rats. Black is dominant over agouti in these rats. As is well 

 known, in the laboratory rat agouti is dominant over black. The colour 

 of the black hybrids, and of the l)lack ?]uropean houserats generally is 

 quite different from the black of the dojnestic rat. It is more nearly 

 like the colour of the dominant black coatcolour iu some I'abbits, studied 

 byPunnett, and called by him black-agouti. The relation between the 

 dominant ])lack and the recessive black in rats has not yet been tested, 

 as no recessive black has yet appeared in the raftus group, whereas 

 crosses between these rats and the domestic rats derived from Mns 

 norvegicus have never yet resulted in young. We may call A the first 

 gene demonstrated by Morgan, the one which distinguishes black from 

 agouti rats in this group. And we will designate with B the second 

 gene, the one which is present in whitebellied but absent from dark- 

 bellied rats. This lastnamed gene is possibly identical with the gene 

 which has become known in work on housemice, and which distinguishes 

 the l)right, intensely coloured chocolates and blacks, and the darker, 

 whitebellied agoutis, from the fade chocolates and blacks and the lighter, 

 darkbellied agoutis. In oui' rats it is probable, that the black rats with 

 B were glossier and more intensely black than those without, but the 

 difference was not as striking as in the housemouse. 



The two females from the cross between Dr Bonhotes male and 

 the Mus rattus female were first mated back to their father, producing 

 37 young of which 14 black, 14 whitebellied agouti, 2 graybellied agouti, 

 1 yellowbellied agouti, 5 yellow, of which one darkbellied, and 1 pearl 

 gray. Of these, 4 were w;iltzers, and 2 of the whitebellied agouti had 

 white tailtips. 



