INSECTA. 809 



die body, and running along its whole length, named trachea. From these 

 tracheal vessels are derived a great many ramifications or bronchi, the num- 

 ber of which is more or less considerable, as they belong to parts enjoying 

 more or less vital energy. The tracheae communicate with the external air by 

 means of openings called stigmata, of which the number varies, placed on 

 each side of the body. In caterpillars, the number of stigmata is generally 

 eighteen. These stigmata are marked in the skin of the insect by a small 

 scaly plate, open in the centre, and furnished with membranes or filaments 

 to protect the entrance. The larva? of many species which live in water, 

 have on the sides of their body, filaments or appendages in the form of 

 laminae, upon which are spread vessels communicating with the bronchi and 

 tracheae. 



Though insects have no lungs, and are destitute of voice properly so 

 called, yet they possess the means of producing sounds. Thus the male 

 grasshopper makes a noise to attract the female. The males of the cicada? 

 and the crickets possess the same faculty. In all these insects, however, 

 the means by which the sound is produced, is similar to that by which a 

 stringed instrument or drum is sounded. The males of the locust and 

 grasshoppers have a portion of the internal margin of their elytra formed of an 

 elastic, transparent membrane, like talc, provided with strong projecting 

 ribs, separated by large hollow spaces. It is a kind of violin, of which the 

 ribs represent the strings ; and the sharp, disagreeable sound by which these 

 insects are distinguished at a distance, is produced by rubbing the elytra 

 over one another. In the cricket, the thigh, furnished with projecting lines, 

 serves as the bow, and the longitudinal ribs of the elytra the strings. In 

 the cicadse, the organ which produces the sound is more complicated. It is 

 a species of drum, and is peculiar to the male. The abdomen, which is coni- 

 cal, is provided below and near the base, with two large semicircular scales, 

 which cover an empty space, in which is a delicate, tense membrane, equiva- 

 lent to the skin of the drum, and below this membrane, at the bottom of the 

 cavity, are other parts, which, striking against it, produce the sound. The 

 stridulous noise which is heard when the Sphinx atropos is touched, is occa- 

 sioned by the air escaping rapidly by the trachea? at the sides of the base of 

 the abdomen, and which is closed in the state of repose by a bundle of stellat- 

 ed hairs. Many coleoptera produce a plaintive and interrupted sound by 

 rubbing the peduncle of the base of the abdomen against the interior walls 

 of the thorax ; and the extremity of the head in others produces a similar 

 sound. The rapid vibration of the wings is the chief cause of the humming 

 noise which most insects produce when flying. 



Insects feed on all kinds of matters, vegetable and animal ; and there is 

 scarcely any production in these two divisions of nature, which does not serve 

 as the food of some insect. Each insect, besides, has a particular food upon 

 which it lives in preference, and which it is endowed with the power of dis- 

 covering and procuring. Many in their perfect state live on food quite dif- 

 102 68* 



