Gordart has reckoned up forty-eight varieties of the fly, without including them all in this enumeration. The multitude of these lively insects, which the first genial sunshine calls forth into life, has limits which the human eye is incapable of exploring. The female fly is easily distinguishable from the male: she is larger than the latter, fuller in the body, of a lighter colour, and, when she is nearly ready to deposit her eggs, the abdomen is so transparent, that they may be perceived lying on both sides, opposite to each other. Nature has instructed her not to deposit her eggs in dry, but in damp substances, which keep them from being dried up, and at the same time afford nourishment to the maggot or worm. The latter issues from the egg generally in twenty-four hours, but, in the sun, within twelve hours after it is laid. About half an hour before, annular circles become visible in the egg, an undulatory motion succeeds, the egg opens at the end, and the warm makes its appearance. Its entrance into the world is extremely tedious; for the three or four minutes taken by the worm to work its way out of the egg, are, for it, certainly so n.any days. It is endowed, on the other hand, with vital powers,-which enable it to defy inconveniences which cost other animals their lives. Nothing but turpentine, the general destroyer of insects, kills it in half an hour. On the fourteenth or fifteenth day, it begins to prepare for its transformation into a nymph, and in this form appears at first of a light yellow, and afterwards of a dark red. You would take it, in this state, for some kind of seed, rather than for the habitation of a living creature. The change of the nymph into a fly requires as much time as the preceding transformation. A thrust with the head then bursts the prison in which it is confined, and the fly, perfectly formed, sallies forth. The sun hastens its birth, which is then the business of but a moment; but in unfavourable weather, this probably painful operation often takes four or five hours. The insect is now as perfect as its parents, and not to be distinguished from them. As soon as it issues from the nymph, it flies away; and only those are unable to use their wings immediately, which have the misfortune to come out in gloomy weather.

Leuwenhock reckons, that every fly has eight thousand hexagons or eyes, on each of the hemispheres composing its face, and consequently sixteen thousand on both. M. Von Gleichen, a German naturalist, observes, that the law of retaliation is in some measure established, in regard to these animals; for if they annoy us, they are in their turn persecuted by others. Small yellow insects, discovered by means of the magnifying glass, crawling among the hairs that grow on their bodies, are supposed to be destined for this purpose.

The fecundity of flies is prodigious. On this head, the last-mentioned naturalist has made the following calculation: -A fly lays four times during the summer, each time eighty eggs, which makes.................. 320

Half of these are supposed to be females, so that each of the four broods produces forty: 1. First eighth, or the forty females of the first brood, also lay four times in the course of the summer, which makes......... ............. 12,800

The first eighth of these, or 1,600 females, three times.................................... 384,000

The second eighth, twice........................ 256,000

The third and fourth eighth, at least one each...... 256,000

Carried forward..........................909 120

Brought forward.......................... 909,120

2. The second eighth, or the forty females of the second brood, lay three times, the produce of which is.................................. 9,600

One sixth of these, or 1,600 females, three times.... 384,000

The second sixth, twice........................ 256,000

The third sixth, once.......................... 128,000

3. The third eighth, or the forty females of the third brood, lay twice, and produce................ 6,400

One fourth of these, or 1,600 females, lay twice more...................................... 256,000

4. The fourth eighth, or forty females of the fourth brood, once................................ 3,200

Half of these, or 1,600 females, at least once...... 128,000

Total produce of a single fly, in one summer. • • .2,080,320