64 Records of the Indian Mtisenm. [Vor<. Ill, 



ments show that they vary from 160 to 197 mm. in length, but seven 

 out of the fourteen are between 170 and 180 mm. The average 

 tail measurement of these seven is about 215 mm. In colour they 

 are all of the common reddish brown tint and resemble one another 

 closely. In no specimen is there an\' white on the abdomen. 



If the results obtained from these places in the Madras Presi- 

 dency be considered together, the}^ show that the races of Mus rattus 

 which occur in the south do not differ from those of other parts of 

 India. It is probable that the rats of Madras city are somewhat 

 smaller, and those of Chingleput somewhat larger than usual. But 

 at Tellicherri, Chitur, Travancore and other places the measure- 

 ments of independent observers sho\A' that the size and proportions 

 of the species are about the same as at Amritsar, Allahabad and 

 Calcutta. The average length of the common rat throughout India 

 is about 170 mm. ; if large numbers of measurements are made in 

 any place it will be found that there are more rats of nearh' this 

 length than of any other length, but that mature rats of 40 mm. less 

 and 40 mm. more than 170 mm. are to be found. Among the rats 

 of the south the colour and quality of the fur is as variable as among 

 those of the north. The most obvious difference is in the fur of the 

 ventral surface, which in some rats is coloured, in others pure w^hite. 

 It seems to the writer to be erroneous to say that there is no specific 

 difference between a white-bellied and a dark-bellied rat. The 

 intermingled distribution of the tw'o kinds makes it almost certain 

 that the dark-bellied form has, from time to time, given rise to the 

 other throughout India ; but the opinion that both must therefore 

 be of the same indivisible species seems to be the outcome of a 

 preconceived idea. Until recentl}^ biologists have held it to be 

 impossible for an animal or plant of one kind (variety or species) 

 to give birth to offspring of another kind. 



There is little doubt that dark-bellied rats occasionall}- give 

 rise to white-bellied offspring ; therefore the two forms must be of 

 the same elementary species, though the difference in their appear- 

 ance is obvious. This seems to have been the line of argument 

 usually followed. 



To say that the two forms are of one race because every in- 

 termediate grade betw^een them could be found by a wide search, 

 is to say nothing against their distinction, for an unbroken series of 

 selected specimens could without difficulty be arranged linking 

 together a small Mus concolor of 95 mm. with a large Mus rattus 

 of 225 mm. To deny the distinction, because the two forms may 

 interbreed, is to deny that there is any racial distinction among 

 mankind . 



It has, a])parently, been proved by the experiments of De 

 Vries and confirmed by others, that a plant of one species can pro- 

 duce offspring of different species. The same possibility is perhaps 

 from time to time in all living things. In the light of this discovery 

 we see that the dark-bellied rats and the white-bellied rats are of 

 different elementary species, and that the former are continually 

 giving rise to the latter in many parts of India 



