1899] ALLEGED NEW MICE 387 
Alleged New Mice. 
The length of the head and body of the largest St. Kilda specimen 
of Mus hirtensis n. sp. is 107 mm. for the male and 110 mm. for the 
female. This is exactly the size of a full-grown Mus sylvaticus in 
Elginshire. The skull of an Elginshire specimen just measured 
(apparently not an old one if we judge from the teeth) is 28 mm. 
long, 1 mm. less than the largest St. Kilda skull. The differences in 
ears and tail do not impress us, and still less those of colour. Even 
in one county Mus sylvaticus shows considerable diversity of coloration. 
At this season, when they sometimes come indoors to supplant the 
house-mouse for a time, specimens are trapped without a speck of 
yellow or brown on the side of neck or belly, while others are of a 
nearly uniform reddish colour on their upper parts with a very distinct 
line of demarcation between the white belly and sides. These are 
minor differences, giving no evidence of more than “individual 
variation.” It may be, indeed, that they are merely “individual 
modifications ” sensu stricto. 
In Texan cornfields Mus musculus sometimes assumes in summer 
the reddish colour of some native species of Muridae, while the belly 
often becomes white or nearly white; the same species caught in 
Elginshire in October sometimes has the belly almost of the same 
colour as the back. It seems impossible to regard these as even 
varieties. 
To illustrate further. A collection was made of an American 
species of Cricetus (Hesperomys), and the individuals were kept in 
captivity for a year or two. They varied in size, but did not vary 
much in colour, which was predominantly brownish grey. A fresh 
capture, however, was reddish, and suggested for the moment—we are 
all open to the temptation—a new variety. After some months of 
captivity it changed to the normal colour of the species. In all prob- 
ability the original difference was simply the result of “ modification.” 
It would be interesting to trap in Sutherland and Skye to see 
whether individuals of the Mus hirtensis type are not to be found 
there, for it is possible that the alleged new species is not the out- 
come of prolonged isolation, but was imported in hay or straw for 
the minister’s horse a century ago. 
The other form Mus muralis un. sp. is interesting on account of its 
colour, but as to its skull characters it appears to us that they will be 
found in perhaps every tenth old specimen of Mus musculus that comes 
to hand. 
Our point, however, is apart from these details. It is that when 
we are dealing with forms for whose characters it would be easy to 
formulate variation-curves, this should not be neglected by those who 
would substantiate their claim to add new species to the British fauna. 
