MISCELIv ANE A . 



MMIMALS. 



The ortginai. home of Mtis decumanus.— ln a previous 

 paper on the rats of Calcutta {Mem. hid. Mus., vol. i, No, i) I 

 called attention to a paper by De I'Isle on the existence of a north- 

 ern negroid race in the Brown Rat {Ann. Sci. Nat. (5), Zool., 1865, 

 pp. 172-222). As my memoir was already in the press before 

 I discovered this paper, I had to content myself with a brief note 

 on the identity of the Indian and European forms of Mns rattus. 

 A fact that caused me some doubt all through the writing of the 

 descriptions of the rats of Calcutta was that M. decumanus, as 

 observed by me in Calcutta and as exemplified by the collection 

 of skins from different parts of India in the Indian Museum, is 

 characterized by a distinct though variable paleness of the lower 

 surface of the tail, whereas in Great Britain the whole tail is of 

 one colour. De I'Isle puts forward a theory which, though it is 

 open to objection on some points, seems to afford a satisfactory 

 explanation of this observation of mine, and to throw light on the 

 problem of the Original home of M. decumanus. His theory, 

 briefly, is that the original wild form of Mus, as exemplified both 

 in M. sylvaticus and M. alexandrinus , has the underparts white 

 or of a light colour and the tail bicoloured (although in the case of 

 M. alexandrinus the tail is of a uniform pale brown) ; but that 

 the corresponding parasitic forms, namely M. musculus and M. 

 rattus, which have attached themselves to man and have there- 

 fore freed themselves from the necessity of protective coloration 

 to some extent, have become dark below and have developed uni- 

 formly dark tails. The second part of his theory is that the change 

 is also due in part to climate, and that under the grey skies of the 

 north the clear and sharp differentiation between the upper and 

 the lower surfaces tends to disappear, and a uniform coloration to 

 be produced. The most marked instance of this is, he says, to be 

 fouid in M. rattus, the northern oft'shoot of the Oriental wild parent 

 form M. alexandrinus. In reference to the climatic change 

 in M. decumanus he merely cites the deviation from type described 

 as M. hihernicus, an occasionally black variety found in the British 

 Isles. In reference to the change in this rat due to parasitism, 

 he writes as follows : — 



" A parasite like the rat (M. rattus) or the mouse (M. musculus), 

 and like these species of Asiatic origin, the Brown Rat C surmu- 

 lot"), which was only introduced into France towards the middle 

 of last century, already exhibits ver^^ evident traces of alteration in 

 colour. Thus one frequently meets with individuals that have the 



