The singing of mice has been attributed to various causes: 1. It has been thought to proceed from disease of the lungs or vocal organs, and to be akin to the wheezing characteristic of asthma. 2. It has been propounded that the singers are always pregnant females; but this statement has been made on very insufficient data, and may, I think, be dismissed. 3. Dr. Crisp informed Mr. Buckland that he thought the singing was caused by a parasite in the liver; and Mr. Buckland tells me that he has at his museum at South Kensington a specimen in spirits in which this parasite is plainly visible in the liver of a singing mouse once alive in his possession. "But," he says, "I am not at all sure that other mice also who are not musical have not this parasite." This I believe to be the case, for it is well known that mice and rats, whether singers or not, are peculiarly liable (perhaps from their promiscuous feeding) to become the hosts of parasites such as hydatids in the liver, and trichina in the muscles.
Of course, I can say nothing about the condition of the livers of the two mice I heard sing last week; but they did not act as if they were afflicted with disease of the liver, or any other organ. Brisk and vivacious in all their movements, darting now and then back to their hiding place, as if to keep open their means of retreat while foraging, they looked the impersonation of vigorous health and bright activity; and, like every one else who has heard them, I feel quite sure that their song—especially that of "Nicodemus"—is not involuntary, nor the result of any disease of the respiratory organs, but an intentional and conscious utterance of a series of notes in musical sequence. As Mr. Buckland says (loc. cit.), "The song is a genuine song, as good and as musical as that of a lark on a fine summer morning,"
Prof. Owen tells us that the anatomy of the mouse is very similar to that of birds; and all who have seen this little rodent in the act of singing have noticed that the throbbing of its throat is like that of a bird in full song, and that it then elevates its snout as a bird does its beak.
Whether the singing of mice may be due to an imitative faculty which leads them to mimic the vocalization of birds, I am not prepared to say. There is great apparent probability in favor of this supposition, but there is, also, strong evidence against it; because well-authenticated instances have been adduced of mice bred in captivity, and apart from any caged bird, having exhibited capability of song.
It is remarkable that in almost every case of a singing mouse having been seen as well as heard, it has been described as very small, much browner than the common gray or slate-colored mouse, and as having very large ears. This exactly applies to my little entertainers, "Nicodemus" and "The Chirper." They are both very tiny mice, their coats are very brown (not so much so as to be fawn-colored), and their ears are abnormally big. I should be tempted to regard the singing mouse as a peculiar variety, if this idea had not been contra-
