62 CROSSING. 



coloured young differ in colour. The two Stizolobium forms, 

 from which Bellings obtained hybrids with burning hairs, 

 differed in the degree of hairiness. 



Recently we observed a case which is quite analogous to 

 Bateson's case in the sweet-pea. Mr Spanjaard, manager of 

 the Ketangoengan sugar factory on Java, sent us some young 

 field- rats of different colours. Among them, was an albino fe- 

 male, who produced numerous wild-coloured young from 

 matings to a male field-rat from Sumatra. These young, when 

 mated together, produced ten albino young and thirteen pig- 

 mented. Only one litter was raised from the original female and 

 an albino son. It contained four albinos and two with pigment- 

 ed eyes, but was destroyed by the mother before it was four 

 days old. Two albino F2 were left to continue the work with. 

 They produced three litters, one of six, the second of five, and 

 the third of three. Not one albino was amongst them, all being 

 pigmented. The only possible conclusion is that the original 

 albino female must have been lacking in two different genes, 

 each indispensable for pigment-formation. The origin of the 

 albino female is unknown. But everything points to it that the 

 group of rats in which she was found were the descendants of 

 a cross. For with the exception of this albino, two black-eyed 

 whites or creams, and two very pale greys were caught, and 

 the inheritance of the waltzing character turning up in the F 3 

 of the albino cross is as complicated as that of albinism. Walt- 

 zing in house-rats we found to be recessive. 



One pair of the coloured young from two albino parents 

 have up till now produced 10 coloured and 6 albinos. A second 

 female had 5 coloured and 6 albinos. The ratio of coloured to 

 albino in the first pair is sufficiently close to a 9 : 7 one, two 

 make the existence of two genes probables. 



In numerous instances new, or comparatively new, charac- 

 ters must be produced by crossing by combining genes, which 

 up to the moment of the cross were present only in different 

 individuals. The presence of the burning hairs en the pods of 

 Belling's hybrids between the Lyon bean and velvet be&n is a 



