WQ Hagedooin. 



with the colours of mice and rabbits, it is probable that this animal 

 was related to chocolate as the silvers to black. The numbers are very 

 much too small to decide anything'. This is a grreat disadvantage in 

 work with rats of this group. Especially in the first generations, 

 comparatively few animals can be induced to breed at all. The litters 

 are large, but very far between, and the mortality among the young 

 animals is appalling. 



Waltzing. 



As we have stated al)Ove, waltzing rats can not be propagated 

 like waltzing mice. The females do not show the slightest interest in 

 the young, which is the most favourable case, or else they mutilate 

 them at the moment of birth. Once we succeeded in obtaining a full 

 litter of young from a waltzing female fieldrat by watching the right 

 moment to take them away to a fostermother. In the houserat-treerat 

 series w^e never obtained a young rat with a whole skin from any 

 waltzing female. 



From a black waltzer with a black normal sister we had one 

 litter, containing 5 normal blacks, 1 ])lack waltzer and 1 agouti waltzer. 



From the same male with a darkbellied agouti sister we had 

 2 black normal young, 1 darkbellied agouti normal, 1 whitebellied agouti 

 normal and 1 whitebellied agouti waltzer. Later on we obtained some 

 more waltzers of different colours in a large cage in which one of 

 the males was a waltzer. and in which were a number of females of 

 different colours. 



In Java, we bred a waltzing yellow male to his normal yellow 

 sister and obtained <\ normal and 3 waltzing yellows. From another 

 yellow sister, which must have been homozygous for either or H or 

 both, he had 6 normal yellow young. 



Young waltzing rats can be sorted out l)efore the eyes are open, 

 in the same way as waltzing mice. When the litter is laid in a row 

 in one's hand, covered with the other hand and quickly turned over, 

 it will be seen that some young rats at once struggle to reverse their 

 position, whereas the waltzers seem indifferent whether they lay on 

 their back or not. 



A great many more crosses were made between rats of the 

 houserat-ti-eerat series, than the ones chosen here to show the in- 

 heritance of the main genes. In many instances single pairs of rats 

 would not breed, so that we had to make up small colonies of two 



