In

hand, the chords or reeds are indeed rectangular, but they are fixed by three sides instead of one. the common reeded instrument, again, we raise or lower the notes by varying its length; while, in the plates of the vocal reeds, it is the size which is varied. In musical instruments, besides, we cannot employ nor procure reeds, the plates of which can every instant alter their thickness and elasticity as happens in the vocal chords. It can easily be conceived, then, from these circumstances, that the vocal chords may produce and vary the tones of the voice somewhat after the manner of reeded instruments, though we cannot make out the analogy in every particular.

M. Majendie partly proved these views by actual observation; and, in the instance of dogs, he found that, when the sound uttered was grave, the vocal chords vibrated through their whole length, and the expired air passed through the whole extent of the orifice (glottis). When the sounds were acute, on the other hand, the vocal chords did not vibrate in the front, but only in the back part; and, as the orifice was of course diminished, the air only passed through the vibrating portion. When the sounds, again, became very acute, the vocal chords no longer vibrated, except at the very extremity, and the expired air then passed out only at this part. So far as he was able to ascertain, the sound increased in acuteness till the orifice became entirely closed. When the air could no longer pass, the sound ceased.

That it is the vocal chords whose vibration produces the sound, may also be fairly inferred from experiments made after death; for by taking the windpipe of any quadruped and blowing strongly from below upwards, no sound will be produced so long as the orifice remains expanded: but if, while continuing to blow, the orifice is compressed so much

they build is called the Boshman's grass, and I believe the seed of it to be their principal food, though, on examining their nests, I found the wings and legs of different insects. From every appearance, the nest which I dissected had been inhabited for many years, and some parts of it were much more complete than others. This, therefore, I conceive to amount nearly to a proof that the animals added to it at different times, as they found necessary from the increase of the family, or rather of the nation or community*"

Nests of the Sociable Grosbeak (Loxia socia).

It will be seen, from the following description of the same structures, that the streets of nests are a mere fancy, though enough of the marvellous remains to gratify the curious. "I observed," says Vaillant, on the way a tree with an

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enormous

nest of those birds to which I have given the appellation of republicans; and, as soon as I arrived at my camp, I dispatched a few men, with a waggon, to bring it to me, that I might open the hive, and examine its structure in its minutest parts. When it arrived, I cut it to pieces with a hatchet, and saw that the chief portion of the structure consisted of a mass of Boshman's grass, without any mixture, but so compact and firmly basketted together as to be impenetrable to the rain. This is the commencement of the structure; and each bird builds its particular nest under this canopy. But the nests are formed only beneath the eaves of the canopy, the upper surface remaining void, without, however, being useless; for, as it has a projecting rim, and is a little inclined, it serves to let the rain-water run off, and preserves each little dwelling from the rain. Figure to yourself a huge irregular sloping roof, and all the eaves of which are completely covered with nests, crowded one against another, and you will have a tolerably accurate idea of these singular edifices.

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Each individual nest is three or four inches in diameter, which is sufficient for the bird. But as they are all in contact with one another, around the eaves, they appear to the eye to form but one building, and are distinguishable from each other only by a little external aperture, which serves as an entrance to the nest; and even this is sometimes common to three different nests, one of which is situated at the bottom, and the other two at the sides. According to Paterson, the number of cells increasing in proportion to the increase of inhabitants, the old ones become streets of communication, formed by line and level.' No doubt, as the republic increases, the cells must be multiplied also. But it is easy to imagine that, as the augmentation can take place only at the surface,

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the new buildings will necessarily cover the old ones, which must therefore be abandoned.

"Should these even, contrary to all probability, be able to subsist, it may be presumed that the depths of their situation, by preventing any circulation and renewal of the air, would render them so extremely hot as to be uninhabitable. But while they thus become useless, they would remain what they were before, real nests, and change neither into streets nor sleeping-rooms.

"The large nest that I examined was one of the most considerable I had anywhere seen in the course of my journey, and contained three hundred and twenty inhabited cells, which, supposing a male and female to each, would form a society of six hundred and forty individuals. Such a calculation, however, would not be exact. I have spoken above of birds among which one male is in common to several females, because the females are much more numerous than the males. The same is the case with many other species, both in the environs of the Cape and in the colony; but it is particularly so among the republicans. Whenever I have fired at a flock of these birds, I have always shot four times as many females as males *"

After the preceding details of what we may well call the marvellous efforts of birds in basket-making, some of our own little mechanics may not appear to much advantage; though their more slender structures are equally suited to their mode of breeding, and exhibit no small skill in the management of the materials. The nests which we allude to are those of several of our summer warblers (Sylviade, VIGOrs), some of which, though built by different species, are so like in appearance, that it requires some experience to distinguish them. Amongst these we may *Vaillant, Trav., 2d series, vol. iii.

it passes into the keel of the breast-bone, which keel is seldom composed of a single bone, but consists of two sides, with a third resting upon them by way of cover, the whole forming a sort of sheath or tunnel. When the windpipe arrives at the extremity of this sheath, it bends downwards in a serpentine form resembling the letter S, and again, beneath the portion just described, it emerges from the sheath, and rising upwards over the middle bend of the shoulderblade, it winds, thus supported, in the manner of a trumpet. Upon its passing under the cavity of the chest, and just before it reaches the lungs, as if to form another vocal organ (larynx), it is transversely cut (being as broad as the small bone is long), and a

The breast-bone of a wild Swan, with part of the keel removed to show the convolution of the trachea within it.

The point of the keel-bone, showing the opening through which the trachea enters and returns.