the common name of the fly-worm bred in flesh, from the egg of the great blue flesh-fly. Notwithstanding the distaste for this animal, its figure and structure of parts are greatly worth attending to; and may serve as a general history of the clasps of worms produced from the eggs of flies.
This animal is white and fleshy: its body is composed of a number of rings, like the bodies of caterpillars and other similar insects; and is capable, at the pleasure of the animal, of assuming different figures; being at times more or less extended in length, and consequently more or less thick.
Notwithstanding that this animal has no legs, it is able to move itself very swiftly; and in its first attempt to move its body, is extended to its greatest length, and assumes something of the figure of a pointed cone. The pointed part of the cone is the head of the animal, and is not separated from the next ring by any deeper furrow than the rest of the rings are from one another. In some states of the animal, one may see two short hooks thrust out from the head; but more generally two scaly hooks are observable: these are, however, sometimes hid, and have each of them a case or sheath; into which the animal can retract them at pleasure. These hooks are bent into an arch, the concavity of which is towards the plane on which the creature is placed; and they are thickest at their insertion in the head, and thence diminish gradually, till they terminate in a fine sharp point.
These two hooks are placed in a parallel direction, and can never come together, and therefore cannot serve in the place of teeth for grinding the food; but merely to pull and sever it in pieces, that it may be of a proper size for the mouth of the creature. Besides these hooks the maggot has a kind of dart, which is about a third part of their length, and is placed at an equal distance between them. This also is brown and feely like them; it is quite straight, and terminates in a fine point. The hooks have as it were two feely thorns at their points; and this dart seems intended, by reiterated strokes, to divide and break the pieces of flesh these have separated from the rest into smaller parts. Immediately below the apertures for the eyes of the hooks, is placed the mouth of the animal; the creature does not show this little opening unless preferred: but if the pressure is properly managed, it will sufficiently open it, and there may be discovered within it a small protuberance, which may very naturally be supposed either the tongue or the sucker of the animal. The hooks in these creatures not only supply the place of teeth, but also of legs; since it is by fastening these hooks into the substance it is placed on, and then drawing up its body to it, that it pulls itself along.
The back of this creature lowers itself by degrees as it approaches the extremity of the belly; and near the place where the back begins to lower itself, are placed the creature's two principal organs of respiration. One may perceive there two small roundish brown spots: they are very easily distinguishable by the naked eye, because the rest of the body of the creature is white; but if we take in the affluence of glaases, each of these spots appears to be a brown circular eminence raised a little above the rest of the body. On each of these spots one may also discover three oblong oval cavities, something of the shape of button-holes; these are situated in a parallel direction to one another, and their length nearly in a perpendicular direction to that of the body of the animal. These apertures are so many stigmata or air-holes; openings destined to admit the air necessary to the life of the animal. It has six of these stigmata, three in each side of its body.
The great transparency of the body of this animal gives us an opportunity also to distinguish that it has on each side a large white vessel running the whole length of the body. It is easy to follow the course of these vessels through their whole length, but they are most distinct of all towards its hinder part; and they are always seen to terminate each in the brown spot above mentioned: this leaves us no room to doubt that they are the two principal tracheæ.
The ramifications of the two great tracheæ are very beautifully seen in this creature, especially on its belly; and it is remarkable, that no vessel analogous to the great artery in the caterpillar clasps can be discovered in these; though, if there were any such, their great transparency must needs make them very easily distinguishable; nor could its dilatations and contractions, if so considerable as in that clasps of animals, be less so.
See ERUCA.
Malpighi imagined, that this artery in the caterpillar clasps was a series of hearts; in its place, however, there may be seen in these animals a true heart. It is easy to observe in these creatures, about the fourth ring of their body, a small fleshy part, which has alternate contractions and dilatations; and is not only discoverable in the body by means of its transparency, but on making a proper section of them in the second, third, and fourth, will be thrown out of the body of the creature, and continue its beats for some time afterwards.