THE GROWTH OF GROUPS 79 



said to be quite white in this respect. The smoke grime, 

 which clings everywhere in a large manufacturing town 

 such as Bombay, explains this slight discrepancy. 



From time to time systematic zoologists have turned 

 their attention towards the rats of India ; they are unani- 

 mous in their opinion that these animals are difficult to 

 classify. The more experienced workers have generally 

 taken a broad view of the subject, recognizing that the 

 group Mus rattus is characterized in particular by the 

 skull, the length of the tail and ears and the pattern on 

 the soles of the feet. Having denned the group by these 

 salient features they have described a great range of 

 variability within the species especially in respect of coat 

 colour. Mr. W. F. Blanford describes Mus rattus in 

 " The Fauna of British India " as follows : " Usually 

 brown, more or less rufous or occasionally yellowish 

 brown ; more rarely blackish brown or black, below 

 generally white, frequently sullied sometimes brown or 

 grey and occasionally with a white, fulvous, or grey 

 median band." 



Any one who has had experience of the subject will 

 know that these words are well chosen to describe the 

 various colours which occur. It was no doubt the purpose 

 of the writer to mention in as few words as possible any 

 variety that might be found. A reader might sum up 

 this description hastily in the following manner. 

 " Roughly speaking, the colour of these animals may be 

 anything." He might suppose that the coat colour of 

 rats afforded an excellent example of variation in all 

 directions, scattering, fortuitous, according as one or 

 other term fitted his conception of the manner of variation. 

 But he would be wrong, I think, in coming to this 



