PEOTECTIVE COLOEATION IN THE HOUSE-MOUSE. 467 



Mus musculus from the mainland of Ireland and from G-reat 

 Britain. Some of the specimens I compared them with were 

 trapped in corn-fields in the Eastern Counties of Ireland, and are 

 certainly not " smoke-stained " as is so often the case with mice 

 caught in houses. From No. 6 onwards they grow gradually 

 lighter, both dorsally and ventrally . No. 9 shows a distinctly 

 rufous colour dorsally, but has the grey belly of the House- 

 mouse ; No. 10, but slightly lighter than No. 9 dorsally, has a 

 very white belly ; and from this point onwards through the series 

 the mice are all various shades of rufous or fulvous grey dorsally, 

 and with the exception of one or two, that retain traces of the 

 grey belly of their ancestors, they are pale buff ventrally. In 

 Nos. 20, 23, 24, 29, and 30 the grey bases to the hairs on the 

 ventral surface have almost or completely disappeared. The 

 specimens numbered 10 to 36, ^. e. all the markedly pallescent 

 individuals, can be broadly described in the following terms : — 

 Dorsal fur much paler than in the domestic type ; rufous grey 

 or fulvous grey is the usual colour. Ventral surface j)ale buff, 

 separated from the darker dorsal fur by a more or less clean-cut 

 line. The slaty-grey bases to the hairs which characterize Mus 

 onuscidus typicus are usually, but not always, reduced both in 

 shade and in extent. All over the body, on the ears and tail, 

 the hairs are generally lighter and more fulvous than in Mus 

 musculus typicus; the ears, nose, and tail are also lighter. The 

 feet are white, or pale buff, in all cases ; in the ordinary House- 

 mouse they vary from smoky-grey to white. The claws are 

 flesh-coloured ; the eyes dark brown. Many of these mice, how- 

 ever, do not fulfil all these requirements, intergrading in some 

 one or more characters with the darker mainland form ; but 

 everybody will admit the difficulties that beset one in describing 

 an unstable aberration that has not yet become stereotyped into 

 a constant subspecies or species. Notwithstanding the perfect 

 intergradation, the mean colour of this race is not only lighter 

 than that of the type, but is lighter than most, if not all, of the 

 light-coloured subspecies of Mus musculus which are preserved in 

 the British Museum. 



During October 1875, I made the following observations on 

 the habits of the mice. They live in burrows in the sandj 

 often of a considerable depth. The nest is made in a chamber of 

 such a burrow ; I dug out three of these nests, all of which were 

 from two to three feet from the entrances, and bad several 



