PRODUCTION OF SOUNDS BY INSECTS.

515

it is occasioned by the striking of its mandibles upon the wood. The sound is evidently intended by the animal as a means of communication with its fellows; for if it be answered it is continually repeated, whilst if no answer be returned the animal repeats the signal in another place. The noise exactly resembles that produced by tapping moderately with the nail upon the table; and, when familiarised, the insect will very readily answer this imitation. The most remarkable example of the production of sounds for the purpose of authority, is that of the Queen-Bee; which has the power of influencing the whole hive, especially about the time of swarming, by the peculiar notes she produces.

Fig. 257.-ANOBIUM.
Natural size and magnified.

678. Many Insects have the power of expressing their passions, also,-as fear, anger, sorrow, joy, or love,-by the sounds they can generate. The most curious of those given out under the influence of alarm is that produced by the Sphinx Atropos or Death's-head Hawk-moth (fig. 258); which

when confined, or taken into the hand, sends forth a strong and sharp cry, resembling, some say, that of a mouse, but more plaintive and even lamentable. The means by which this cry is produced, have not yet been certainly ascertained. The influence of anger, sorrow, and joy, in modifying the tone of the hum of Bees, is well known to those who have studied their habits; the first is particularly evident in the sharp angry tone which is heard when the hive has been disturbed, especially if some of the Bees have been killed; the second

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SOUNDS PRODUCED BY INSECTS.

is manifested in a low plaintive tone which is given-out when the queen has been taken away; and the cheerful humming which is immediately heard when the sovereign is restored, is an evident indication of the last. Of all the Insects inhabiting this country, the most noisy are the Crickets; whose

Fig. 259.-HOUSE-CRICKET.

sound, which seems to be their expression of love, is produced by the rubbing of the elytra or wing-covers one against the other. In several species it may be distinctly seen that a very strong nervure on one of these has a jagged surface like that of a file; and that this works against a collection of smaller nervures, which resemble so many strings.

679. The Cicada (fig. 260) was a very favourite insect among the ancient Greeks; and was frequently mentioned by their poets with the most endearing epithets. Its song was considered particularly musical; and it was regarded as the happiest as well as the most innocent of animals. The Cicada of other countries produce an extremely shrill and disagreeable sound, which can be heard at a great distance. In the warmer parts of the United States, there is a species which, in the hotter months of summer, is a very troublesome and impertinent neighbour. The Cicada of Brazil are said to be audible at the distance of a mile this is as if a man of ordinary stature, supposing his powers of voice increased in the ratio of his size, could be heard all over the world. The organs by which the sound is produced are placed on the under side of the body, between the base of the hind legs and the abdomen, and consist externally of a pair of large flattened plates of a horny texture, varying in form in the different species. When these are raised, they are found to conceal a large cavity partially covered with a membrane of a

SOUNDS OF INSECTS.-VOICE OF VERTEBRATA.

517

much more delicate nature than the external covering, with a horny plate in the middle, which lies along the bottom. Still more internally are two bun

dles of muscles, which are the real agents in producing the sound; for, when they are pulled and suddenly let go, even in a dead specimen, the sound is produced as well as though the insect were alive. They draw-in and force-out, by their alternate and rapid contraction, a horny drum or membrane, stretched in such a manner as to vibrate readily; the sound occasioned by the movements of which passes out through an aperture resembling the sound-holes of a violin. The Fulgora, also, have considerable sound-producing powers, but exert them in the night, whilst the Cicada perform in the day. The Great Lanternfly of Guiana (§ 400, fig. 175) begins regularly at sunset; and its noise, resembling that of a razor-grinder at work, is so loud, that the insect is called "scare-sleep" by the Dutch colonists.

Fig. 260.-CICADA.

680. In all air-breathing Vertebrata, the production of sound depends upon the passage of air through a certain portion of the respiratory tube, which is so constructed as to set the air in vibration. In Reptiles and Mammals, it is at the point where the windpipe opens into the front of the pharynx, that this vibrating apparatus is situated. Few of the animals of the former class, however, can produce any other sound than a hiss, occasioned by the passage of air through the narrow chink by which the trachea communicates with the pharynx; but this sound, owing to the great capacity of their lungs (§ 325), is often very much prolonged. Among Mammals, on the other hand, there are few, if any, which have not some vocal sound; but the variety and expressiveness which can be given to it differ considerably in the several tribes of this class, being by far the greatest in

518

STRUCTURE OF THE LARYNX.

Man. This sound is produced by the apparatus termed the larynx, which is situated beneath the base of the tongue, and in front of the pharynx (§ 192, fig. 107). It is suspended, as it were, from the hyoid bone (h, fig. 261),—a bone of a horse-shoe form, detached from the rest of the skeleton; from two projections () on the upper side of which, several of the muscles of the tongue originate. The sides of the larynx are formed by two large cartilages (t, fig. 261), which

are termed the thyroid cartilages; where these meet on the middle line a projection is formed, which is particularly prominent in Man, and has received the name of Pomum Adami, or Adam's apple (a). The thyroid cartilages rest upon another, termed the cricoid (c); this has the form of a ring, much deeper behind than in front, and surmounts the trachea, with the upper ring of which its lower edge is connected by a membrane. Upon the upper surface of the back of the cricoid cartilage, where there is an open space left between the two thyroid cartilages, are mounted two small cartilaginous bodies, the arytenoid (ar, fig. 262). These are movable to a certain extent; and their position may be changed in various directions by several muscles which act upon them.

STRUCTURE OF THE LARYNX.

519

681. To these arytenoid cartilages are attached two ligaments of elastic fibrous substance (§ 23), which pass forwards to be attached to the front of the thyroid cartilage, where they meet in the same point. These are the instruments concerned in the production of sound, and also in the regulation of the aperture by which air passes into the trachea; and they are termed the vocal cords or ligaments (fig. 263, li). By the meeting of these ligaments in front and their separation behind, the usual aperture has the form of a V; but it may be narrowed by the drawing-together of the arytenoid cartilages, until the two vocal ligaments touch each other along their whole length, and the aperture is completely closed. In this manner, the amount of air permitted to pass through the larynx is regulated; and a protection is afforded against the entrance of solid substances. An additional guard is afforded by the doubling of the lining membrane, in such a manner as to form a second pair of folds (ls, fig. 263), above the preceding; and over the space between these (which is much wider than that between the vocal cords) there is a valve-like flap, the epiglottis (e, fig. 262), which is pushed-down upon it in the act of swallowing, so as to prevent the entrance of solid or fluid particles into the space beneath, which is called the glottis. From the causes formerly mentioned (§ 193), such particles are occasionally drawn into the glottis; and they excite, by a reflex action, an involuntary and extremely violent cough, which tends to expel them again. Sometimes, however, solid bodies of no inconsiderable size find a lodgment in the wide spaces (v, fig. 263) between the upper and lower pair of ligaments, which are termed the ventricles of the larynx; and occasionally they pass through the opening between the vocal cords, which is termed the rima glottidis or fissure of the glottis, into the wind-pipe.

682. In the ordinary acts of inspiration and expiration, the arytenoid cartilages are wide apart, so that the aperture is as large as possible; but for the production of vocal sounds, it is necessary that the aperture should be narrowed, and that the flat sides, rather than the edges, of the vocal ligaments should be opposed to one another. This is accomplished by a peculiar movement of the arytenoid cartilages, occasioned by the contraction of certain muscles. When these ligaments are thus brought into position, the air in passing through the