"In shape," write Messrs. Kirby and Spence, "this little boat pretty accurately resembles a London wherry, being sharper and higher, to use a nautical phrase, _fore_ and _aft_; convex below and concave above; floating, moreover, constantly on the keel or convex part. But this," they add, "is not all; it is, besides, a _life-boat_, more buoyant than even Mr. Greathead's. The most violent agitation of the water cannot sink it; and what is more extraordinary, and a property still a desideratum in our life-boats, though hollow it never becomes filled with water, even though exposed to the torrents that often accompany a thunder-storm. To put this to the test I yesterday placed half a dozen of these boats upon the surface of a tumbler half full of water. I then poured upon them a stream of that element from the mouth of a great bottle held a foot above them, yet, after this treatment, which was so rough as actually to project one out of the glass, I found them floating as before upon their bottoms, and not a drop of water within their cavity."
[Illustration: _Rubbish Towers of the Sand-Wasp._]
Some insects make the homes of their young in the earth. Of these, the insect called the sand-wasp forms, perhaps, one of the most interesting examples. This insect selects generally a hard sunny sand-bank for the excavation it is about to accomplish. Armed with a pair of powerful jaws, by means of which the insect can break off good-sized fragments of the rock she is about to mine, she sets to her arduous undertaking with a bold heart, and it is not long before a tolerable cavity is scooped out. Many of our readers have seen the manner in which human miners proceed when they are forming a hole in a lime or other rock, for the purpose of blasting, and must have noticed that they are in the habit of using a little water, in order to facilitate the boring operation. We are all, also, familiar with the tale of Hannibal chemically softening the Alpine rocks by means of vinegar. The little insect in question has been instructed by the great Creator also to adopt a means of shortening her labour, for it has been observed that she moistens the rock by letting fall a drop or two of fluid upon it from her mouth. By this means her work goes on rapidly. The rubbish soon begins to accumulate. It will be scarcely conjectured what this patient labourer does with it. Were we to look narrowly at the sand-bank which such wasps frequent, we should find on its surface a number of curious little projections like horns, rising from the surface. These are towers built by the sand-wasp of the pieces of rubbish which she scoops out of her mine. She cements them together, and, instead of throwing them away, she lays the masses in regular order until they have assumed the appearance here shown. It has been supposed she does this with a view to keep out enemies and to keep her progeny cool; just as in a tall house the cellar is its coolest apartment, so the height of the tower in question seems to be an additional protection against the rays of the scorching sun. After it has deposited its egg at the bottom of the excavation, the sand-wasp sets out on a foraging expedition, and hunts about until she finds certain green caterpillars. Seizing upon one of these she flies with it to her mine, and then returns for more prey. After collecting about a dozen of these helpless beings, fixing them so that they are hopeless captives inside her dark prison, she bids farewell to the egg, for the future well-being of which she has thus assiduously provided. She takes down her tower of stones, and, with the materials which composed it, fills up the entrance to the cell, thus shutting in both the prisoners and their future devourer in a common dungeon, there to await the changes which time will inevitably bring about.