in natural history, that part of the fly-clasps which is analogous in its situation to the breast in other animals. Many have called it the breast in the albo, but improperly; because the breast of other animals is the place of the lungs and trachea, but these organs are in the fly-clasps distributed through the whole body. The wings are affixed to this part of the fly-clasps; and there are some distinctions of great consequence in regard to the arrangement and distribution of these animals into genera. Some flies have a double corcelet, or one divided into two parts; and this is the case of the fly produced from the formica leo, which therefore does not carry its only distinction in the figure of its antennae. One pair of the legs of this fly are attached to the first or anterior corcelet, which is also capable of moving on the other.

The corcelets of some flies are also much more elevated than those of others; and in some this elevation is carried so far, that the head is forced by it to be bent downward, and the creature is plainly made hump-backed by it. The great kind, and the tijule, furnish instances of this elevated and hump-backed corcelet.

A series of flies of two wings are known by a very particular armament which they carry on the corcelet, usually called their brevifl. This consists of two long, slender, sharp-pointed prickles, which are immovable in their insertions, and seem meant as offensive or defensive weapons; but in what manner they are used it is not easily to be determined.

All these flies are produced from long water-worms, with with open and funnel-fashionioned tails, or furnished with their aperture for respiration at the hinder extremity.

There are three known species of this sort of fly, with armed corcelets, which differ much in size, but are all produced of worms of this kind. The largest of these flies are produced from the largest and longest worm, and are something longer than the bee. The smallest are produced of worms very small and slender, and are themselves extremely minute; and the third kind is of a middle size between these, and produced from a proportionably smaller worm than that of the first, and proportionably larger than that of the second species.

All these species have their wings but little distinguishable at their first production from the shell; they appear indeed only like two slender filaments laid across their bodies; but they quickly show, that in this state they were only very nicely folded together; and soon expand, and show their full extent and proportion.

When first produced from the shell, these flies are of a pale green colour. The under part of their belly in many continues green, but in the greater number it becomes of a pale dead brown. Some of them have the outside of their bodies of a deep brown, approaching to black, with lines of a dead brown between the commissures of the rings. The back of some others has only a blackish brown band, which runs straight down from the corcelet to the end of the body, the whole body beside being of a dead brown. The corcelet in these flies is brown, and the prickles are yellowish near their insertions, but nearly black at their points. They have three of the small glossy eyes disposed in the shape of a triangle on the back part of their head; and their reticular eyes are brown, and at some distance from one another.