140 ZOOLOGY. 
capable of motion than the thorax, and in some insects it is very flexible, 
as in the coleoptera with short elytra, the wasps, &e. 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 system of insects corresponds with the articulate type, being 
composed 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 luminots at night. Among 
these are members of the genera Elater and Lampyris. 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 abdomen 
are luminous also. The light is sufficient to enable a person to read small 
print, if the insect be passed along the lines. In Lampyris the light 
proceeds 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 
larvee 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 the 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 phosphorescence 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 disturbed; 
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 
way. The genus Brachinus, when disturbed, shoots ont a vapor accom- 
panied by aslight 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 
Papiho project, when disturbed, a forked gland from the neck above, which 
is the seat of a very offensive 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 
against the inside of the elytra, and the prothorax against the mesothorax. 
The male Cicada 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 
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