8o THE MICROSCOPE. 



numerous forms of these instruments. In the bees, 

 wasps, hornets, ants, the last segment of the body is 

 provided with a sting ; the ichneumon, saw-flies, gall- 

 flies, are furnished with an ovipositor; in external 

 form there is not very much difference between an 

 ovipositor and a sting. The sting consists, in wasps, 

 bees, &c., of two very sharp dart-like organs, with 

 barbed teeth at their points ; this apparatus is enclosed 

 in a horny, elongated sheath; near the root of the 

 sting you will find a membranous bag, which contains 

 a poisonous fluid ; between the darts there is a canal, 

 down which the venom is poured into the wound 

 made by them. The ovipositors of insects differ 

 somewhat in form, but they all consist of a long tube 

 protected and covered by a cleft sheath. That curious 

 hymenopterous insect, not uncommonly met with in 

 this country, the Sir ex gigas, and generally taken for 

 some kind of hornet by the ignorant of such matters, 

 has a very strong ovipositor, by means of which the 

 insect can bore into hard timber. The Cynipidtz, or 

 gall-insects, so extremely common on various parts of 

 the oak, have a very delicate ovipositor, with a toothed 

 edge ; using this instrument as a kind of saw, the little 

 insect bores a hole in some part of the tree, and 

 deposits therein its egg. It is supposed that some 

 irritating fluid is dropped into the hole at the same 

 time as the egg, which produces what are known as 

 " galls." These serve both as shelter and food for the 

 young grubs of the gall-flies. You will be struck with 

 the beauty of the spiracles and tracheal system of in- 

 sects, the apparatus by means of which the respiration is 

 carried on. In insects the blood is oxygenated by the 

 admission of air into every part of the body, even into 

 the most minute; the air enters through the spiracles, 

 which are situated at each side of the body, and pass- 

 ing down the tracheae, which branch off into numerous 



