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Quadrupeds. 



half-bred, and afterwards with less and less qualities of the snake-rat, till at length all 

 traces of it disappeared. In the language of horse-breeders, the new " strain of 

 blood" was " bred out" or eliminated, or, more correctly, it was overpowered by the 

 repeated crossing- always on the line of the common brown rat. Had the circum- 

 stance been reversed, and a few of the Mus decumauus had escaped among a multitude 

 of M. Alexandrinus, the characters of the latter would undoubtedly have prevailed in 

 the end. The capacity for interbreeding appears to be endless and indefinite. There 

 are sorts of rats which will not come within the category of those recognized, or as 

 their intermediate crosses. We have in this country a black rat with a white chest; 

 in the British Museum are two stuffed rats, chestnut coloured with white breasts, 

 which were captured in Cambridgeshire. The distinguished Irish naturalist, 

 Mr. W. Thompson, has described a black rat with a white chest as a new species, 

 under the name of Mus Hibernicus. On the occasion of the reading of my paper on 

 the cranium of the snake-rat, it was suggested by Mr. Lubbock that it might be a 

 "variety" of one of our other rats. Subsequently, in a discussion in the 'Field" 

 newspaper, by which a great deal of interesting information regarding rats was 

 brought out, Mr. Newman put forward the idea that these cosmopolitan rodents are, 

 in their differences, not so many species, but mere " geographical races," and I am 

 much inclined to believe that this is the truth of the matter. Certainly, if inter- 

 breeding and a resultant fertile offspring determine the specific identity of varying 

 , individuals, there is an end of the question. The different rats do interbreed, and 

 their progeny are fruitful for any length of time and any number of generations. 

 Rats hold a curious intermediate position between wild and domestic animals. They 

 are not absolutely either, and they are both. They are wild as they are their own 

 masters and roam at will ; they approach a domestic condition, inasmuch as they are 

 nearly always associated with man, and are indirectly dependent on him for their food. 

 Rats are cosmopolitan — they inhabit nearly, if not quite, every region where the 

 human race dwells. In violation, or at least not in keeping, with their dentition and 

 organs of primary assimilation, rats are omnivorous : they can live entirely on animal 

 food; they can even resort to the predaceous habits of Carnivora; or they may have 

 the barest vegetable diet for their sole sustenance. Such constitutional capacities and 

 such adaptability of habit afford wonderful conditions for the development of races. 

 Mus Alexandrinus appears to be spreading all over the world ; its extreme agility and 

 the ready way in which it accommodates itself to shipboard naturally tend to such a 

 result. Besides the eastern localities where it was first found, according to Blasius, 

 it was obsened by Savi in Italy, in 1825, and named by him Mus lectorum ; it was 

 found by Pictet near Geneva, in 1841, and described by him under the title of Mus 

 leucogaster ; Blasius states that he himself saw it at Antibes, in the South of France, 

 and he repeatedly obtained it from the Alps in South-Eastern France. It has also 

 been taken at Stuttgard ; and Riippell mentions that it has been sent to him from 

 America. In this country it has beeu known to rat-catchers in the neighbourhood of 

 the docks both of London and Liverpool. — Journal of the Proceedings of the Linnean 

 Society, Vol. vi. p. 66. 



