Now these are the "Laryngeal sacculi" which, according to Mr. Illingworth, produce the falsetto voice by "acting in the same way as a hazel-nut can be made to act as a whistle, when the kernel has been extracted through a small hole in the shell," &c. I think, however, that the reader will, from the description given above, agree with me that the acoustic properties of the pockets of the voicebox cannot be very great, and that, at all events, there is a vast difference between their construction and that of a hazel-nut, either with or without the kernel. Then there is this additional difficulty, that even if one could whistle upon the pockets in the manner suggested, there are two of them, covered, let it be remembered, with a multitude of glands, continually producing moisture, and liable to enlarge or to diminish. How, I should like to know, could two such cavities be so tuned as under any circumstances to produce exactly the same tones? Would not rather frightful discords be the inevitable result? And again, what provision is there in the pockets for the gradations of pitch? But quite apart from these considerations, this and other similar theories are completely disproved by the fact that every tone which the human voice is capable of producing can be produced by _inspiration as well as by expiration_. The tones sung by inspiration are, as might be expected, wholly devoid of beauty, because the vocal apparatus is, as it were, put upside down, and the position of bellows and resonator reversed. But that does not alter the question. The fact remains, and clearly proves that the pockets have no more to do with the falsetto than with the chest voice, because in inspiration the air strikes the vocal ligaments _after it has passed_ the pockets, and yet the result is, beauty of tone apart, exactly the same. The function of the pockets, in my opinion, is this: They are the means of isolating the vocal ligaments, thus enabling them to vibrate freely and without hindrance. They also allow the sound-waves to expand sideways, thereby materially adding to their resonance. Lastly, they with their many little glands produce and supply the vocal ligaments with that moisture without which, according to the investigations of J. Mueller,[H] the production of tone cannot be carried on.