THE GROWTH OF GROUPS 47 



is situated in the tile-like scales and short hairs, is 

 present equally both on the upper and lower surfaces, 

 Fig. 2,a. Departures in more than one direction from 

 this type, however, occur ; they will be described as 

 follows : 



(a) (Bi-coloured type, Fig. 26). Pigment may be 

 absent from the lower half of the circumference of the 

 tail, from base to apex. This condition is found in 

 several established species of Mus which inhabit moun- 

 tainous districts. The only well-known example in 

 India is the rat of Kashmir, Mus vicerex. The character 

 also occurs in smaller local groups in other parts of the 

 Himalayas. Judging from the distribution of this cha- 

 racter, we may be sure that every rat possessing it is 

 not of one and the same line of descent. The character 

 h'as appeared on many occasions, almost always in 

 mountainous regions. A single individual with this 

 peculiarity was, however, found in Rangoon. 



(6) (Semi-bicoloured type, Fig. 2c). In this type, as 

 in the last, there is no pigment in the lower surface, but 

 the pigmentation of the upper surface does not extend 

 the whole length of the tail ; it comes to an end at a 

 point somewhere about the middle. Rats possessing* 

 this peculiarity have been recorded from places so far 

 removed from one another as Tenasserim, Manipur, and 

 Naini Tal. Wherever found they have been called Mus 

 berdmorei ; although, in my opinion, there is no reason 

 for supposing that their direct relationship is any closer 

 than in the case of others, which do not possess a special 

 feature in common. 



(c) (The parti-coloured type, Fig. 2d). In this type 

 there is total loss of pigment in the whole circumference 



