[Illustration: Larva of the common Gnat floating in water, greatly magnified. _aa_, the body and head of the larva; _b_, the respiratory apparatus, situated in the tail; _c_, the larva, not magnified.] "They are hatched in a few days, and then the boat of empty eggs floats about until it is destroyed by the weather. And to show you how good a boat it is, I will tell you what a gentleman did to prove it. Mr. Kirby, who is very fond of natural history, and has written a great deal about insects, says that he put half a dozen of these gnat-boats in a tumbler half full of water, and then poured upon them a stream from the mouth of a quart bottle, held up a foot above them, and he could not sink them. More than that, the water would not stay in them. If you push one to the bottom with your finger, it will come up to the top directly, and you cannot see any water in it." "Why, this is a noble boat, Uncle Philip, that will never sink." "True, boys; but listen, and you will find that before it can use its wings the gnat has to sail in another boat still, much more dangerous than this is. After it is hatched, it has to pass through several shapes before it gets to be such an insect as you see. Here is a picture which will show you its different shapes. [Illustration] "The first is the same which you saw in the last picture, only in this drawing the head is uppermost. But its last change, when it becomes an insect with wings, is the most curious part of the whole. When it is about to get its wings, and become a perfect gnat, it raises its shoulders just above the top of the water, and its skin cracks, so that the head of the gnat immediately comes through. The shoulders come next, and make the crack larger; but it has yet all its body to get out, and its legs and wings are as yet all shut up in its case. Now is the time of danger for the gnat. It raises itself nearly straight out of the crack, and by wriggling works its body along: and if a particle of water should get upon the case, or touch its wings, it would be overset, and must perish. Thousands and thousands die in this way. It is so very light, too, that the wind will drive it about, and whirl it round and round upon the top of the water; and when it is almost out, the insect is tossed about in a canoe or boat of the very weakest sort, while its body is a mast, which appears much too large for so small a boat. At last it gets far enough out of the case to stretch its fore-legs, and put them down upon the water (which will bear a gnat's weight), and then it is safe; it spreads its wings, and soon leaves the little boat which was so dangerous. Here is a picture of the gnat getting out of its case." [Illustration] "Well, Uncle Philip, all this is very strange; we never knew before that the gnat was a sailor."