1907.] Dr- Hossack: The Rats of Calcutta. 5 



with the colour variations of the Black Rat, its tendency to white breast patches, al- 

 binism, etc. further on I shall show, as has already been noted in Bombay by Liston, 

 that an extreme range of colour is found in the Mus rattus of the large cities of India, 

 from black through brown to yellow and white. Size is another characteristic that 

 is very variable, as has been already noted in the case of M. jerdoni and M. alexandrinus ; 

 this also will be gone into fully in the case of M. rattus. With regard to minute 

 variations in skulls, such as the shape and size of the bullae, the shape of the inter- 

 parietal, the form of the coronoid suture and the like, one can only come to the con- 

 clusion that they are frequently unworthy of consideration. The faintest variations, 

 such as " bullae a shade flatter," " nasals rather narrower," " incisive foramina 

 rather narrower, " are made specific. Fortunately many observers are becoming 

 convinced of the futility of these minute differentiations. 



Skin Measurements. — There is a very considerable error in attempting to estimate 

 the size of an animal from a skin. Invariably, whether there has been stretching of 

 the skin or not in drying, it will be found that its dimensions have greatly increased, 

 while the tail, if without the vertebrae, has shrunk correspondingly. There is a stuffed 

 skin of Nesokia bengalensis in the Indian Museum which measures 27-5 cm. in 

 length of head and body ; judging from the size of the hind foot 35 cm.), it probably 

 measured when fresh only about 20 cm. Similar instances might be multiplied, but the 

 fallacy of skin measurements is too well recognized to necessitate more. Nevertheless, 

 one still finds descriptions of new species and genera where the only measurements 

 given are those of dried skins. The errors arising from accepting the measurements of 

 spirit specimens may be considerable. Thus Blanford notes that in the case of three 

 specimens of Golunda ellioti, the Indian Bush Rat, there was a shrinkage of no less 

 than 20 per cent, in the length of the head and body after they had been kept four 

 months in spirit. 



Change of Colour in Specimens — In comparing with type skins and specimens, 

 it must be remembered that specimens in alcohol, or specimens exposed to light or 

 even kept for very long in a drawer, change colour. Anderson has noted the tendency 

 to become rufous in Nesokia, and Barrett-Hamilton notes the same in the case of Mus 

 sylvaticus. It is very marked in many of the skins of the Indian Museum, particularly 

 in those of Nesokia and M. decumanus. Though agreeing in all other respects 

 with the stock descriptions, they have developed a general rufous foxy tint all over. 

 In spirit specimens minor colour variations become extremely ill-marked in a very 

 short time, so that a white tip to the tail or a white breast spot may become almost 

 unnoticeable in the space of a month or two. 



From what has been said it is evident that some more rational system of classi- 

 fication is required. This is rather an urgent matter considering the extreme practical 

 importance of the subject in connection with plague. It is now twenty-five years 

 since Mr. Oldfield Thomas reduced chaos to order, earning the thanks of every 

 worker who has approached the subject. Is it too much to hope that he will again 

 take it up, brush away the accretions of a quarter of a century, and give us a classi- 

 fication free from the redundancies and overlappings that at present exist ? 



