THE GROWTH OF GROUPS 115 



So from one point of view they are separate species, but 

 yet no one who had taken them from the traps could have 

 regarded them otherwise than as belonging to the same 

 family circle. They must have been more nearly related 

 to the black-tailed rats of the Nainital bazaar, than to 

 animals living in such distant places as Mergui or Manipur, 

 Khatmandu or Kashmir. 



Some interesting problems therefore arose out of the 

 capture of this couple. Accordingly steps were taken to 

 obtain others of the same group. Six more were obtained 

 from the same house and the adjoining outhouses. All 

 were deficient in caudal pigmentation. Three were 

 strictly in the condition of berdmorei as regards caudal 

 pigmentation, that is to say, the dorsal pigmentation 

 extended up to the middle of the length of the tail or 

 slightly beyond it, but in the other three it did not extend 

 so far. Later on, seventeen more white-tailed rats were 

 caught in other isolated houses. In sixteen of them, the 

 pigmentation reached a variable distance along the tail 

 but fell short of the tip. In one other it reached as far 

 as the tip (bicoloured type) ; this was the second specimen 

 obtained from Nainital, which, from the taxonomist's 

 point of view, ought to be called vicerex. The two were 

 captured in separate houses situated about a mile apart, 

 in both cases they were found living along with rats 

 having tails of the semi-bicoloured type. It is probable 

 that if a pair of rats with completely bicoloured tails had 

 been selected artificially for breeding, they would have 

 bred true to their type and given rise to offspring of the 

 type vicerex. However, it is evident that at the present 

 day the berdmorei type is the commonest among the rats 

 living in the outlying houses of Nainital, and that the type 



