140 ZOOLOGY. 



capable of motion than tLe thorax, and in some insects it is very flexible, 

 as in the coleoptera with short elytra, the wasps, ifec. The abdominal 

 spiracles are situated at the junction of the dorsum and venter, or in the 

 lateral margin of the dorsum, and nearly every segment has a pair of 

 spiracles. The abdomen has various appendages, as the forceps in the 

 male of Panorpa, hooks, stylets, ovipositor, sting, &c. 



The nervous si/stem of insects corresponds with the articulate type, being 

 f'omposed of a double cord with a line of ganglions. The principal organ 

 of circulation is a dorsal vessel, which is a long muscular pulsating heart. 

 The alimentary canal offers many modifications to adapt it to the various 

 kinds of food upon which insects subsist. 



Many insects, particularly the Coleoptera, are luminous at night. Among 

 these are members of the genera Elater and Lami^yris. In both sexes of 

 certain species of the former genus, the light is emitted chiefly from a 

 raised oval spot on each side of the pronotum, but the sides of the al)domen 

 are luminous also. The light is sutiicient to enable a person to read small 

 print, if the insect be passed along the lines. In Lampyris the light 

 l)roceeds from the posterior extremity of the body, and it is more bright in 

 the female (which is sometimes apterous) than in the winged male. The 

 larv» of some of the Lampyrides are luminous, and in the southern United 

 States there is a small flat larva (probably of an Elater) about an inch 

 long, which emits a strong phosphorescence from all tlie segments, equal to 

 that of Elater noctilucus ; and when the head and tail are brought together, 

 a brilliant circle, like a ring of diamonds, is formed. According to Kirby 

 and Spence, the eyes of some nocturnal Lepidoptera are luminous. In 

 several North American species of Sphinx we have observed eyes 

 apparently phosphorescent, by dim candlelight, or when shaded from its 

 direct light ; but this false piiosphorescence has always disappeared when 

 the light was extinguished, so that in these cases, at least, there was only a 

 peculiar reflection. 



Many insects imitate the possum in simulating death when disturljed; 

 some allow themselves to drop from leaves ; elaters, when unable to escape 

 by running, either simulate death, or by a click throw themselves out of the 

 w-^ay. The genus Brachimis, when disturbed, shoots out a vapor accom- 

 panied by a slight sound. Some insects defend themselves by biting, some 

 by stinging, some by ejecting acrid matter from the stomach and mouth, 

 and others by exuding a disagreeable scent. The caterpillars of the genus 

 Papilio project, when disturbed, a forked gland from the neck above, which 

 is the seat of a very oftensive odor. The spinous tufts of some caterpillars 

 have an irritating quality like that of nettles. 



Sounds are emitted by various insects, and by means of various organs, 

 as the rubbing together of the wings in Orthoptera, the end of the abdomen 

 ao-ainst the inside of the elytra, and the prothorax against the mesothorax. 

 The male Ckada makes a very loud and shrill sound, which is produced 

 by a peculiar apparatus opening at the base of the abdomen. The vibrat- 

 ing apparatus is lateral, and the mirror-like membranes within the external 

 aperture may be destroyed without interrupting the sound. A nocturnal 

 344 



