CRANIAL CHARACTERS OF THE SNAKE-RAT. 



71 



any animals, not domesticated, are ever liable to snch individual 

 differences in the most important osteological characters as these 

 skulls have exhibited. 



Whether this rat has long been an inhabitant of this country — 

 whence imported, if imported (which I think most likely) — are 

 questions that I cannot at present answer. The rat corresponds 

 very closely with the Mus Alexandrinus of Geoffroy St.-Hilaire, 

 and will very probably turn out to be the same. It has been 

 known for many years to those who trade in rats for sporting 

 purposes, but has probably been hitherto confounded by scientific 

 men with the old Black Eat of this country. 



Note. — Since the foregoing was written, I have had reason to 

 conclude that the Snake-Eat is certainly the same species, race, or 

 variety as was first described by Geoffroy St. Hilaire under the name 

 " Mus Alexandrinus" But at the same time my further investiga- 

 tions into this subject have convinced me that our knowledge of the 

 rats of Great Britain, or of rats in general, is not so satisfactory or 

 definite as descriptions in works on Natural History would lead 

 us to suppose. Undoubtedly, characteristic specimens of M. rattus, 

 M. decumanus and M. Alexandrinus may be obtained ; but there 

 are intermediate forms in endless variety, as any one may satisfy 

 himself by an inspection of the cages of a rat-catcher after his visit 

 to the rat-homes about the docks of London. There can be no 

 question that the typical forms enumerated above as three species 

 are constantly being merged and reduced, under favouring con- 

 ditions, by interbreeding : the most superficial observation of 

 many specimens will convince any one of this fact. This circum- 

 stance was demonstrated some years since at the Zoological Gar- 

 dens, Eegent's Park. Some individuals of Mus Alexandrinus, 

 which had been sent from Alexandria, got loose in the gardens ; 

 and for a long time afterwards the keepers frequently caught 

 cross-bred rats, at first half-breds, and afterwards with less and less 

 of the character of the Snake-Eat, till at length all traces of it dis- 

 appeared. 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 Eat. Had the circumstance been reversed and a 

 few of the Mus decumanus had escaped among a multitude of M. 

 Alexandrinus, the characters of the latter would have undoubtedly 

 prevailed in the end. The capacity for interbreeding appears to 

 be endless and indefinite. 



