H 4 THE GROWTH OF GROUPS 



one occasion from the Oriental region. When found the 

 name M. berdmorei has always been applied to them. In 

 regard to this species we read in " The Fauna of British 

 India " " tail bicoloured, the upper surface of the basal 

 half brown, the lower surface of the basal and the whole 

 of the terminal half pale with white or whitish hairs, the 

 type comes from Mergui, specimens have since been 

 obtained from Moulmein, Manipur, and the Khasi hills." 

 There is no doubt that the species has been recognized 

 when met with by the peculiar colouring of the tail, for 

 there is no other definite character by which it could be 

 recognized. Hence it has been the custom to regard all 

 rats with tails in this condition as descendants of a common 

 stock, wherever they may have been found. If we are 

 to carry on this custom we ought to regard the individual 

 under discussion and others like it from Nainital as of the 

 same stock. 



For similar reasons, its companion ought to be regarded 

 as Mus vicerex, for when compared side by side with a 

 Kashmiri rat the only appreciable difference lies in the 

 general colour of the fur, which is slightly redder than in 

 the rats of Nainital. The short bicoloured tail, the white 

 belly and the dense fur are characters common to both 

 which give them a remarkable degree of resemblance. 

 It is probable that if a pair of rats with completely bi- 

 coloured tails had been captured in Nainital and sent 

 to a museum in Europe for identification they would have 

 been placed either in the species vicerex or niveiventer, if 

 this last is still a recognized species. Similarly, if a pair 

 with semi-bicoloured tails had been sent they would have 

 been called berdmorei. In accordance with the rules of 

 systematic zoology they ought to be treated in this manner. 



