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“Every one knows that the oar-blades of swimming beetles always go up and down simultaneously and in regular time. On the other hand, as soon as one puts a Dyticus on the dry land, i.e. on an unyielding medium, it uses its hind legs entirely after the manner of other land insects; that is, they are drawn in and extended again alternately, as takes place clearly enough from the footsteps in Fig. 119, A. We learn from this that water insects have not yet, from want of practice, forgotten the mode of walking of land insects.

“The forcing up of the water as a propelling power is added to the repulsion produced by the strong strokes of the oars. If the beetle stood up horizontally in the water, he would be lifted up.

“As the trunk, however, assumes an oblique position when the insect wishes to swim, one can then imagine the driving up of the water as being divided into two forces, one of which drives the body forward in a horizontal direction, while the other, that is, the vertical component, is supplied by the moving of the oars. The swimming insect is thus, as it were, a snake flying in the water.