414 THE AMERICAN NATURALIST [Voi>. LI 



short tail and dark belly, with the Egyptian tree-rat, Mus 

 tectorum, a fulvous-agouti smaller rat with a long tail 

 and white underparts, sharply demarcated. The young 

 were all like tectorum. These animals, on being mated 

 inter se, gave some dark-bellied young, and from the 

 mating of two 'Hectorum" young he obtained, together 

 with some dark-bellied and white-bellied agoutis, a few 

 orange yellow rats. At this stage we took over his. ani- 

 mals. Through the excessive zeal of the French custom- 

 officers, who feared that the animals might carry mala- 

 ria ( !), they were returned from Dieppe to London, and 

 most of them died on the way, including all the yellow 

 ones. When finally the rats reached us in Verrieres, we 

 obtained only a few white-bellied animals. 



White-bellied female no. 13 finally mated in the big 

 room with a black French Mus rattus male, after having 

 killed a great many males in cages. The hybrids were 

 black and had very long tails. We lost a good many in 

 transporting the animals from France to Holland. 



One of the white-bellied agouti rats obtained, tree- 

 footed number 17, was mated to two black hybrid females, 

 24 and 25, and with tectorum female no. 19. From the 

 mating of 17 with 24 we obtained twenty young, of 

 which seven were blacks, seven white-bellied agouti 

 (like tectorum), five yellows and a few pearl gray. 

 Among the blacks one had a white tail tip, and one of 

 the white-bellied agoutis had also a white tip to the tail. 

 Three of the gray-bellied agoutis were waltzers. These 

 animals behave exactly like waltzing mice. They run 

 around in small circles with amazing rapidity, and they 

 are unable to climb. But whereas waltzing mice are less 

 viable than their normal litter brothers, the waltzing rats 

 are as vigorous as normals. And whereas waltzing mice 

 are congenitally deaf, our waltzing rats can hear per- 

 fectly normally. 



From the mating of male 17 with foiiialo 2o we obtained 

 seventeen young, seven blacks, (if wliidi oiio waltzer and 

 one white-throated, seven white Ix'llii'd aumiti, two gray- 



