Читать книгу A Text-book of Entomology онлайн

136 страница из 232

“This plane, in conjunction with the rectilinear ‘movement’ (no) obtained by the retraction of the tibia, produces a path (nr), and this is what is actually described by a painted foot upon a properly prepared surface, as a sheet of paper;^[22] supposing, however, that the body in the meantime is not moved forward by other forces. In the last case, and this indeed always takes place in running, the trunk is moved a bit forward, together with the leg which is just describing its curve with a rapidity corresponding to the momentum obtained; the result of this is that the curve of the foot from its beginning (n) to its end (a) bends round close to itself, just as a man who, when on board a ship in motion, walks across it diagonally, and yet on the whole moves forward, because his line of march, uniting with that of the ship, results in a change of position in space.

“The case is the same in the middle and hind legs, which must make a double course also, yet in such a way that the straight line is drawn, not during the retraction, but during the extension; during which, however, quite as in the fore leg, the members mentioned (R3) gradually approach the body.