66 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVI. 



Like other murines, this species shows, within certain limits, an 

 almost startling plasticity. Its structure responds readily to the 

 demands of purely local requirements. If necessary colour or the 

 quality of the coat are modified ; a change in diet induces modifi- 

 cations in the development or the " set " of the muscles of 

 mastication ; and these in turn mould the skull, or lead to the 

 lengthening or shortening of the tooth-rows. 



Considerations such as those mentioned in the preceding 

 paragraphs lead us to realize the hopelessness of attempting to 

 disentangle the history of the rats in large towns or ports like 

 Calcutta or Bomba3^ In such places the rat population is a 

 motley horde, representing the progeny of truly native rats crossed 

 with the descendants of old wanderers and with newcomers not 

 only from the neighbouring hinterland but from all parts of the 

 world. It is therefore only in the more remote parts of the 

 country that we can reasonably expect some measure of success to 

 crown such efforts. 



The material collected by the Mammal Survey is most extensive, 

 and although gaps exist it is now possible to gain a broad idea 

 of the chief facts relating to the distribution and variation of the 

 present species in India. Save for the conclusion that 11. nitidus 

 in entitled to full specific rank, the conclusions of this paper 

 are little more than natural extensions of those reached by 

 Thomas in 1S81, upon the basis of comparatively insignificant 

 material. 



In North-Western India, Sind and the Punjab, the prevalent 

 race seems to be identical with R. r. alexandrinus. Further east, 

 from the Himalayan districts of Kumaon and Sikkim southwards 

 to Travancore and Ceylon, and through Assam and Burma to 

 bouth Tenasserim, the common rat is that called " var. rvfescens" 

 by Thomas aiid Blanford. This is, however, split into a number 

 of local races. The most striking and widespread variations are 

 those to which attention has so frequently been drawn in the 

 Reports, viz., a dark bellied variety and a variety with pure white 

 underparts. Mr. Wroughton has already commented upon the re- 

 markable distribution of these two types (Report No. 15, /. B. 

 N.H. 8., Vol. XXIII, p. 295). 



At the higher collecting stations in Kumaon only white bellied 

 specimens were found ; at some lower stations white and dark bellied 

 rats w^'re present together in apparently equal numbers ; while at 

 still lower elevations dark bellied rats alone occurred. Again in 

 Sikkim and at Hasimara, Bhutan iJuai's, all are of the white bellied 

 type, although a certain proportion have slaty bases to their ventral 

 hairs. In Bengal and Orissa, and in the southern part of the penin- 

 sula as at Travancore, as well as through Assam, Burma, and Tenas- 

 serim, the ratss are uniformly of the white-bellied type. From South 



