CRANIAL CHARACTERS OF THE SNAKE-RAT. ae 
any animals, not domesticated, are ever liable to such 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 Rat of this country. 
Note.—Since the foregoing was written, I have had reason to 
conclude that the Snake-Rat 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 IZ. rattus, 
MM. 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, Regent’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- Rat, 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 Rat. Had the circumstance been reversed and a 
few of the Mus decwmanus had escaped among a multitude of IL. 
Alexandrinus, the characters of the latter would have undoubtedly 
prevailed in the end. The capacity for interbreeding appears to 
be endless and indefinite. 
