It is my purpose, on my return from Africa, to set on foot a series of such experiments, with the hope of ascertaining the facts connected therewith. And while in Africa I shall aim to make such records of the natives as to ascertain whether their speech conforms to the same laws of development or not. It is my earnest hope to be able to do the same thing with the great apes which I am going chiefly to study. I think if I can record on a phonograph cylinder the sounds uttered by a young chimpanzee under certain conditions once each day for a year or so, I can determine whether there is a like growth in their speech, and to what extent the same laws control it. I have already observed that the quality of voice in a given species of monkey changes with his age very much in the same manner as the human voice; but I have not been able to follow the changes through one individual specimen by which to ascertain the exact manner of such change. [Sidenote: SOUNDS OF BIRDS] The sounds of birds have been studied perhaps more than any others except those of man, but they have not been studied as speech, nor to ascertain their meanings. Their musical character has attracted attention and been the subject of some discussion. My opinion is that much that has been said on that subject belongs more properly to the realm of poetry than of science. I think the sounds of birds are chiefly intended for speech, but it may supply the place of music in their æsthetic being; but, so far as I have observed, I confess that I cannot find that they obey the laws of harmony, melody, or time, and it is my opinion that most of the efforts to write the sounds of birds on a musical staff are not to be relied upon as accurate records of the sounds. There is no doubt that each sound uttered by a bird is in unison with some note in the chromatic scale of music, but the intervals between the tones of the same bird do not coincide with those of the human voice. It is quite evident that birds possess an acute sense and ready faculty for music, and many of them show great aptitude in imitating the sounds of musical instruments; some varieties of birds, such as the southern mocking-bird, the thrush, and others, imitate with great success the sounds of other birds. They often do this so perfectly as to deceive the species to which the sounds belong. The songs of birds, as they are called, appear to afford them great pleasure, and they often indulge in them, I think, as a pastime; the effect is pleasing to the ear because of its cheerfulness, and it is not discordant or wanting in richness of tone in most birds. From the little study I have given them I think it safe to say that the range of sounds possessed by any one bird is quite limited and their notes are strictly monophones. This last remark does not apply to the sounds made by parrots and birds of that kind.