1909.] R. E. Lloyd : The Races of Indian Rats. 47 



In order to be able to express the amount of difference in 

 appearance between the members of these groups, the writer as- 

 certained b}' trial the longest distance at which a person of normal 

 vision could distinguish the three kinds from one another. It was 

 found that in a good light the three could be easily named at a dis- 

 tance of thirty yards, and less easil}^ even up to fift}'' yards. 



On the one hand, we have seen in discussing Mus listoni and M. 

 comheri , that at the present day species are founded on such small 

 differences that the fact of their being at all appreciable by the 

 naked eye is considered noteworthy, while on the other hand we 

 now see that differences which are appreciable at a distance of 50 

 3^ards are not considered of specific value. This is the natural 

 outcome of the conviction that organisms of an}' ]3articular 

 species — elementary or indivisible — can only give birth to off- 

 spring of the same species. This conviction is of course based 

 on the common experience that like as a rule gives birth to like. 

 The belief that there are no exceptions to this rule is so strong that 

 evidence afforded by the eye cannot be believed, and certain species 

 have been considered indivisible but polymorphic. Mus rattus 

 is one of these. All who have written about Oriental rats are 

 agreed that the common brown Mus rattus {alexandrimis or rufescens) 

 usually has a brown belly, but that there is a second form w-ith a 

 white bell3% and some have justly considered that the black rat is 

 merely a third form. But all have regarded the two or the three 

 forms as one indivisible species. It has been felt that to regard 

 them otherwise w^ould be to admit the discontinuous and manifold 

 origin of species. 



Although it is difficult to gauge the general opinion of biolo- 

 gists from the writings of individuals, it seems that this admission, 

 so distasteful to many, is gaining in favour at the present day ; 

 the evidence afforded by the rats of India seems to be in favour of it. 



Hardwar. 



Mr. Pitambar Paul has sent a useful collection of fifty Mus 

 rattus in alcohol, with measurements of each. 



The lengths of these range from 140 to 200 mm. A large number 

 of immature individuals have been included, but there are more 

 rats of 180 mm. than of any other length. If their lengths are 

 arranged according to their frequency they show the same kind of 

 diagram as text-fig. 2, in which the measurements of a large num- 

 ber of immature rats were included. 



As regards colour they are all of the brown dark-bellied type 

 found commonly throughout Northern India ; two of them are 

 white-bellied with a broad coloured stripe in the middle line of the 

 breast and abdomen. 



Ballia. 



The Civil Surgeon of Ballia has sent a typical dark-bellied Mus 

 rattus. 



