1909.1 R- E. Lloyd : The Races of Indian Rats. 93 



naturalists, having discovered an isolated group of melanotic rats, 

 would speculate as to what part of the world they or their progeni- 

 tors had wandered from. It seems to the writer that the discontinu- 

 ous distribution of species (using the actual meaning of the word 

 for ' ' anything that has ever received a specific name ' ' ) can often 

 be explained without postulating means of emigration. 



A list of sports or groups of sports has been drawn up, but 

 other cases have been described which have perhaps an equal right to 

 a place on the list ; such cases are Pjb. 2, Ota. 2, Alh. 3, Mds. 4, 

 Tci. I, Rng. lb, Rng. yb and c, Rng. 8a. In some of these cases 

 the differences which mark off the groups are smaller than in others. 

 We have also seen that all the rats living in a particular house 

 (or set of burrows), although closely resembling one another, 

 often show, in certain features, recognisable differences from the 

 mean of the race, although these differences are so small that they 

 fall within the range of normal variation of those particular 

 features exhibited by the general population. The differences 

 which mark off these groups are small, but the groups showing them 

 are very common. These small differences seem to be equivalent 

 to the " family likenesses " of mankind, heightened perhaps by 

 inbreeding. 



It is interesting to consider the commonness of sports and groups 

 of sports. Within a week at least four were met with in Rangoon. 

 The total number of sports mentioned in this paper was selected 

 from among not very many thousands of rats. The number of 

 rats present in India and Burma must be some thousands of millions. 

 Four thousand rats a day were destro5'ed in Rangoon for some 

 months without producing much effect on the rat population which 

 in that city alone must be several millions; over a million have 

 already been killed there. Sports, therefore, must exist in large 

 numbers, each with a small chance of forming a " family group," 

 each of which has a very small chance of forming a race. In the 

 different magnitude of their chances lies an explanation of the 

 well known fact that rare species are many and common species are 

 few. 



In the writer's opinion ' ' family groups ' ' of sports have been 

 frequently met with by naturalists who have described them as 

 new species. Such species can seldom be rediscovered; they be- 

 come extinct after a fitful survival through a few generations. 

 They remain in our literature, however, as rare species. The chances 

 of a " family group ' ' developing into a race seems to be very 

 small indeed. For while among the rats of India the birth of 

 sports seems to be of daily occurrence, the number of established 

 races is very small, though from its superfluity a race is much more 

 likely to meet the eye than either a family group or a single sport. 



In India we have sure evidence of only four established races 

 of the Mus rattus type. 



Race I [Mus vicerex ?). — In Kashmir most of the house rats 

 have white under parts and relatively short tails which are devoid 

 of pigment below. It has been said that they are of the species 



