92 Records of the Indian Museum. [Vol. Ill, 



or three generations. The variation in the character is, however, 

 different in degree from that which is known as normal variation. 



The ' ' discontinuous distribution ' ' of rats with white under 

 parts, bicoloured tails, and of melanotic rats in the Oriental region 

 is most interesting ; it has been already dealt with , but some of the 

 facts may be shortly reviewed. White-bellied rats form a pure race 

 in Rangoon (Rng. 2) ; the^^ are common in Calcutta. Out of sixty- 

 nine villages in the Punjab it was found that only three contained 

 them in small numbers. The rats of Simla bazaar and of several 

 other places on the flanks of the Himalayas are nearly all of this 

 t3^pe. A few were obtained from Cawnpore and other places ; 

 they form more than half of the rats received from Tellicherri. In 

 many other places, however, they do not occur, and it cannot be 

 doubted that the commonest type of Mus rattus in India is the dark- 

 bellied one, and that the white-bellied type occurs sporadically 

 {vide antea, pages 65, 80). 



Rats with bicoloured tails, although rarer, show the same 

 sort of distribution. There is a pure race of them in Kashmir, 

 There is a race in the Eastern Himalayas (M. jerdoni). They have 

 been recorded from Katmandu (M. niveiv enter) and trom Simla 

 (M. vicerex), but it is doubtful whether they persist as a race in 

 these two places at the present day (see p. 6). This year a small 

 colony of them was met with in Naini Tal (A^^apata race)', and one 

 specimen was found in Rangoon. They have been frequently 

 met with in the southern part of the Oriental region, in the Malay 

 States and Archipelago, chiefl}^ from hill}^ districts. Wherever 

 met with they have shown other slight peculiarities, for they have 

 been described as different species. But the bicoloration of the 

 tail is admitted to be the most important character in all of them. 

 In the two places Rangoon and Naini Tal where the writer met 

 with rats of this sort they did not differ, except in the one respect , from 

 the common local races of those places from which they are thought to 

 have been derived. 



Passing now to the cases of melanism, we find that black rats 

 are not uncommon in Bombay [17]. They occur rarel}^ in Calcutta. 

 We have received pure black rats from Cawnpore and Freemantle 

 (Australia). There is an interesting semi-melanotic type among 

 the Tellicherri collection. Ten pure black mole-rats were ob- 

 tained from two adjacent houses in Rangoon. From the same town 

 we have melanotic examples of Mus concolor, the miniature form 

 of Mus rattus. It cannot be that the black Mus rattus gave rise to 

 the black Mus concolor ; and the brown rattus to the brown concolor. 

 Melanism must have been acquired independent!}' by these two 

 races. 



After considering their discontinuous distribution it seems 

 difficult to believe otherwise than that these three characters, 

 melanism, albi-ventralism and caudal bicoloration, have arisen in- 

 dependently in several places, and are continually arising unnoticed 

 in thousands of other places. It is somewhat difficult to know how 

 far this view is accepted at the present day. It appears that some 



