Because, though possessed of nerves, they have nothing similar to our brain and spinal cord, the two sources of our nerves of feeling and of motion; but, instead of this, they have a chain of ganglia, or bundles of nervous substance, and from each of these bundles, nerves branch out to the parts contiguous, each ganglion forming the centre of feeling to the parts to which its nerves run, or having its own set of nerves.
Many curious particulars connected with the great tenacity of life in insects are mentioned by entomologists, as well with a view to illustrate the animal economy, as to defend their favourite pursuit. Riboud stuck different beetles through with pins, and cut and lacerated others in the severest manner, without greatly accelerating death. Leuwenhoeck had a mite which lived eleven weeks transfixed on a point for microscopical observation. Vaillant caught a locust at the Cape of Good Hope, and after excavating the intestines, he filled the abdomen with cotton, and stuck a steel pin through the thorax, yet the feet and antennae were in full play after the lapse of five months. A decapitated beetle will advance over a table, and recognize a precipice on approaching the edge. Colonel Pringle decapitated several libellulae, or dragon-flies, one of which afterwards lived for four months, and another for six; and, which seems rather odd, he could never keep alive those with their heads on above a few days. Mr. Ha worth, the well-known English entomologist, being in a garden with a friend who firmly believed in the delicate susceptibility of insects, he struck down a large dragon-fly, and in doing so he unfortunately severed its long abdomen from the rest of its body. The mutilated insect after this devoured two small flies. Mr. Haworth then contrived to form a false abdomen, by means of a slender portion of a geranium ; after which the dragon-fly devoured another fly, and, on being set at liberty, it flew away with as much apparent glee as if it had received no injury. It is well known to practical entomologists, that large moths found asleep during the daytime, may be pinned to the trunks of trees without their appearing to suffer such a degree of pain as even to awake them. It is only on the approach of the evening twilight that they part ix. c seek to free themselves from what they must no doubt regard as an inconvenient situation.*
* See Encyclop. Brit., art. Animal Kingdom, vol. iii. 7th edit. 1831.
Considerations such as those glanced at in the preceding page can never, of course, be so misconstrued as to afford any palliation to wanton or inconsiderate cruelty to the brute creation.
Because, in insects, the skin serves the double purpose of protection and support, and represents the cutaneous and osseous system of the latter. Its structure appears much more simple than in the higher classes, as it can neither be said to possess a mucous or cellular web or true skin. It bears the nearest resemblance to the cuticle of the skin of the higher classes, or, rather, all the laminae of perfect skins are here incorporated into one uniform plate. In some genera it is soft and pliable; while, in others, as some of the weevils, it approaches the consistence of bones, or appears as a calcareous crust in the crabs. In some species it is elastic, in others brittle. - (Fleming.) Again, the coat, composed of several portions, moving on one another like the pieces of a gauntlet, also serves to protect the insect from, the effects of various accidents.