276 Miscellanea. [VOL. I, 



under- surf ace no longer whitish, but ash-coloured, with scattered 

 blackish hairs, and the tail not of two colours, white below, as in 

 the type of the s]-)ecies, but uniformly blackish grey." 



Before discussing the pros and cons of De I'lsle's theory, it 

 may be pointed out that he recognizes M. decumanus as a rat of 

 eastern origin characterized by having a tail of two colours. Its 

 most extreme departure from type, as found in the melanotic form 

 known as M. hibcrnictts, he believes to be due to climatic environ- 

 ment ; the minor alterations, shown mainly in the darkening of 

 the under-surface of the tail, he credits, on the other hand, to the 

 effects of parasitic life. Though this theory is a fascinating one, 

 it is not to be accepted without reservations, and there are points 

 in it to which exce])tion may be taken, especially in view of the facts 

 and observations recently collected. The strongest point in its 

 favour is that what he describes as the " wild " type of coloration 

 is almost universal in wild animals of every sort and is now well 

 known to have great protective value. In favour of the climatic 

 part of the theory is the fact that in Calcutta, although I have 

 examined thousands of specimens, I have never come across one 

 that showed a tendency to general melanosis, but have frequently 

 noted the ashy grey belly which he quotes as an instance of the 

 parasitic type of coloration. The strongest argument against the 

 whole theory is that he assumes that the typical form of M. 

 alcxandrinus exhibits what he calls the " wild " type of coloration. 

 This is probabl3' far from being the case, for Liston has shown that 

 no less than 20 per cent, of the rats of Bomba}' are black, while 

 here in Calcutta, while black rats are rare, nearly half of the speci- 

 mens I have collected have grey or orange-grey bellies. Mus 

 (iccumanus, if of eastern origin, should be wild in the East, but I 

 have come to the conclusion that it is even more strictly parasitic 

 on the banks of the Hughli than it is on the banks of the Thames. 

 In Bengal, and in India generally, it is hardly to be found except 

 in seaports and, occasionally, on the banks of the great navigable 

 rivers that debouch at these ports ; in the interior of Bengal and 

 Assam, as I learn from Capt. Gourlay, I.M.vS., and others, it is prac- 

 tically unknown. Why should this be if it is living nearer to its 

 original home than in Great Britain ? Again, if reliance is to be 

 placed on De I'lsle's theor}^ of parasitic versus " wild " coloration, 

 it might be expected that Nesokia hcngalensis, which in Calcutta is 

 a parasitic rat, would show a marked difference when living under 

 purely natural conditions. So far as I know, it shows no such 

 difference. Doubtless this is one of the points that will be taken up 

 in the proposed survey of the rats of India. Another point worthy 

 of investigation would be the question whether Mus rattus exhibits 

 a greater tendency of " wild " coloration when living in trees than 

 it does when living in human habitations. 



W. C. HOSSACK. 



Colour change in Hylobates hoolock, Harlan. — It is generally 

 believed that the variation of colour to which this species is subject 



