1909.] R. E. Lloyd : The Races of Indian Rats. 67 



The rattus group. 



After a brief examination of any large number of rats received 

 at a collecting station, it was easy to separate out those belonging 

 to the species Mus decumanus and Gimomys hengalensis, as well as 

 the mice and shrews. But when these had been set aside, a large 

 number remained which resembled one another in having long 

 pointed snouts, long tails, large ears and six foot pads, one of 

 which was much elongated ; that is to say, in possessing those 

 features well known to be characteristic of Mus rattus. Among 

 many hundreds examined, however, not one was found which in 

 colour and size together resembled any of the Indian rats. 



A large number of measurements of the rats of this group were 

 made, care being taken that only adults were selected, that is to 

 say, those with prominent teats or testes. The teats of any 

 seemingly adult female rat appear in one of three conditions. 

 Firstly, they may be very small and hidden among the fur ; 

 secondly, they may be larger and surrounded by sparse fur, so 

 that they are apparent without search ; thirdly, they may be even 

 more prominent and at the same time red. The first and second 

 conditions cannot be confused. Female rats with teats in the first 

 condition (ver}' small and hidden among the fur) were considered 

 to be maidens and were rejected, even though they were in some 

 cases larger than those having teats in the second condition. 

 Rats with teats in the second condition were considered to have 

 borne young ones at some time. Those in the third condition were 

 advanced in pregnancy. Only those in the second and third con- 

 dition were regarded as adults and measured. Examination of the 

 other generative organs confirmed these opinions. Among males 

 those with testes projecting far behind the anus were counted as 

 adults. It has been asserted that the testicles of rats enter the 

 scrotum only during the rutting season. This view does not, 

 however, commend itself, for it has been shown beyond doubt that 

 in India rats breed all the year round, nor does it seem possible at 

 any time to find an old male of the rattus group devoid of promi- 

 nent testicles^ For the purposes of these measurements, all rats of 

 whatever size devoid of prominent testes were rejected as immature. 

 It was very necessary to select undoubted adults for measurement. 

 Among the group there seemed to be at least two races, a small dark- 

 bellied race and a large white-bellied race, but immature members 

 of the larger race were sometimes smaller than mature members of 

 the smaller race. 



A large number of rats selected with these precautions were 

 measured immediately after death by chloroform. The writer 

 measured sixty of them, selecting equal numbers of the two races. 

 The measurements arranged in series are shown on plate v ; 

 although there is some intermingling towards the middle of the 

 series, nearly all those of the dark-bellied type are in the lower 

 half, those of the other type being in the upper half. 



In order to illustrate the separation of the two races more 

 fully, 500 adult members of the long-tailed races were subsequently 



