The Boat naturally reminds us of the Boatman. In the two gnat-boats which have been described there is no propelling power used or needed, the little vessel floating about at random, and its only object being to keep afloat. But there are many cases where the propelling power is absolutely essential, and where its absence would mean death, as much as it would to a ship which was becalmed in mid ocean without any means of progress or escape. There are, for example, hundreds of creatures, belonging to every order of animals, which are absolutely dependent for their very existence on their power of propulsion, and I believe that there is not a single mode of aquatic progression employed by man which has not been previously carried out in the animal world. There are so many examples of this fact that I am obliged to select a very few typical instances in proof of the assertion. Taking the Oar as the natural type of progression in the water, we have in the insect world numerous examples of the very same principle on which our modern boats are propelled. And it is worthy of notice, that the greater the improvement in rowing, the nearer do we approach the original insect model. The first which we shall notice is the insect which, from its singular resemblance to a boat propelled by a pair of oars, has received the popular name of WATER-BOATMAN. Its scientific name is _Notonecta glauca_, the meaning of which we shall presently see. It belongs to the order of Heteroptera, and is one of a numerous group, all bearing some resemblance to each other in form, and being almost identical in habits. Though they can fly well, and walk tolerably, they pass the greater part of their existence in the water, in which element they find their food. Predacious to a high degree, and armed with powerful weapons of offence, it is one of the pirates of the fresh water, and may be found in almost every pond and stream, plying its deadly vocation. Its large and powerful wings seem only to be employed in carrying it from one piece of water to another, while its first and second pairs of legs are hardly ever used at all for progression. The last pair of legs are of very great length, and furnished at their tips with a curiously constructed fringe of stiff hairs. The body is shaped in a manner that greatly resembles a boat turned upside down, the edge of the elytra forming a sort of ridge very much like the keel of the boat. When the creature is engaged in swimming, it turns itself on its back, so as to bring the keel downwards, and to be able to cut the water with the sharp edge. From this habit it has derived the name of Notonecta, which signifies an animal which swims on its back. The first and second pairs of legs are clasped to the body, and the last pair are stretched out as shown in the illustration, not only looking like oars, but being actually used as oars.