The House Mouse exhibits a considerable range of variation in colour, both darker and lighter than the type, and many of these variations have been bred from and their peculiarities perpetuated and accentuated in confinement as "fancy" mice. Of these the most familiar are the White Mice, really albinos with pure white fur, pink eyes, feet, and tail. There are also dark, nearly black variations, and spotted examples. Sometimes one is surprised at night to find that the house is tenanted by a musical mouse that runs up the scale in what appears to be an attempt at a little song. It has been ascertained, however, that these so-called singing mice are afflicted with a form of asthma, and the supposed vocal efforts are merely the manifestation of their physical trouble. We have had experience of musical mice in another way. For several nights in succession weird sounds came from the pianoforte which suggested that fairies were using it as a harp, twanging the wires instead of striking them with the hammers. An examination of the interior seemed to indicate the actual performer, for a little pile of Spanish nuts, stolen from the table, was discovered inside; and the twanging of the notes was caused probably by the mouse climbing them. A trap baited with a shelled nut put a stop to these performances. Bateson mentions several cases of hairless Mice, except for a few whiskers. A local race of the House Mouse found in St. Kilda is sometimes dignified with species rank under the name of _Mus muralis_. Its distinguishing features include less slender feet and tail, and slight peculiarities of the palate. [Illustration: _Pl. 60._ _G 94._ *House Mouse.* Mus musculus.] [Illustration: _Pl. 61._ _G 95._ *Alexandrine Rat.* An alien stowaway from North Africa.] *Black Rat* (_Epimys rattus_, Linn.). Not many years ago a good deal of modified regret was expressed because it was thought that the Black Rat--the real old British Rat as it was called--was being exterminated by that vulgar upstart the Brown Rat--the Hanoverian or Norway Rat. These laments were mainly called forth by its comparative scarcity in old London warehouses where it had formerly been very numerous. One would have thought it a matter for rejoicing that there was a possibility of our having only one species of the rat pest to contend with instead of two. The disappearance of the Black Rat was remarked by Pennant as far back as 1778. However, later observations tend to show that the Black Rat is far from being extinguished even in the City of London, where the old type of warehouse is being rapidly replaced by ferro-concrete erections with carefully trapped drains. The intelligence of the Rat is equal to little impediments of that sort, and if it cannot get in by way of the basement it can climb walls and enter by the attic windows.