734 RODENTIA— RATTUS 



I. Rattus rattus. 



Since the account, at p. 592, of the Geographical Variation of this 

 species was published, the house rats of India, Burma, and Ceylon have 

 been studied by Hinton (/. Bombay N.H.S., 28, pp. 59-88, 384-416, 716- 

 725, 906-918, 1918 and 1919). This work was based upon the rich 

 material gathered during the mammal survey of India, undertaken by 

 the Bombay Natural History Society, as well as upon the collection in 

 the British Museum. In the various Mammal Survey Reports published 

 by Wroughton and others in the Journal cited, the Indian house rats 

 were listed as " Epimys rufescens " when they had dusky bellies, and as 

 " Epimys rufescens, var. " when their under parts were white. That this 

 difference in colour had some geographical value had long been 

 apparent; and it was thought that the white-bellied and dark-bellied 

 types might belong to two distinct sub-species or even species. To 

 test this possibility was one of the chief objects of Hinton's work. The 

 results arrived at may be briefly summarised as follows : — 



The common Indian house rats, whatever may be their colour, 

 are all referable to R. rattus; but the forms described as R. nitidus 

 Hodgson, and R. vicerex Bonhote, about the status of which there has 

 been controversy, are distinct species of the R. rattus group. 



Like their European representative R. r. frugivorus in the Medi- 

 terranean region, the Indian white-bellied forms of R. rattus Q' Epimys 

 rufescens, var." of the Survey Reports) are essentially wild animals, often 

 living out of doors in jungle and woodland in the most remote rural 

 districts of India, Burma, and Ceylon. As wild mammals they show 

 a definite geographical variation, so that many sub-species have now 

 to be recognised. Descriptions of these are given in Hinton's paper. 



With regard to the dark-bellied Indian house rats the case is 

 different. Wroughton {Journal cited 23, p. 474) had already put 

 forward the view that the white-bellied forms of R. rattus in the Indian 

 region represent the primitive wild form of the species, while the dark- 

 bellied types have developed from these wild forms in response to 

 changes of environment which have ensued upon the species becoming 

 partly or wholly commensal with man, — the darkening of the under 

 parts in the least modified of the Indian races, no less than the 

 darkening of the back in the wholly parasitic R. r. rattus, being 

 the outward indication of domesticity. These dark-bellied forms 

 ("£. rufescens" of the Survey Reports) are in great measure restricted 

 to the districts of India which possess substantial houses ; and they 

 are far less frequently caught out of doors than are the white-bellied 

 races. Series of dark-bellied specimens from single localities or 

 colonies are frequently very uniform in appearance and structure 

 among themselves ; but when series from different, though sometimes 

 neighbouring localities are examined, an enormous range of variation 



