[34]. Von Lendenfeld, however, points out the fact that Straus-Durckheim proved that the wings of beetles are moved by a complicated system of numerous muscles. “In the Lepidoptera I have never found less than six muscles to each wing, as also in the Hymenoptera and Diptera.” “The motions of the wings of Libellulidæ are the combined working of numerous muscles and cords, and of a great number of chitinous pieces connected by joints.”
[35]. Heymons, however, denies that the so-called cerci in Odonata are such, and claims that they are the homologues of the “caudal processes” (superior terminal appendages of Calvert), because they arise from the tenth abdominal segment.
[36]. Amer. Nat., iv, December, 1870.
[37]. Handbuch der Zoologie, p. 17, 1863, Fig. 162.
[38]. In my account of the anatomy of Melanoplus spretus, 1st Report U. S. Entomological Commission, p. 259, I have called these the infra-anal flaps or uro-patagia.
[39]. It has been suggested to us by A. A. Packard that the power possessed by insects of transporting loads much heavier than themselves is easily accounted for, when we consider that the muscles of the legs of an insect the size of a house-fly (¼ inch long), and supporting a load 399 times its own weight, would be subjected to the same stress (per square inch of cross-section) as they would be in a fly 100 inches long of precisely similar shape, that carried only its own weight; from the mechanical law that, while the weight of similar bodies varies as the cube of the corresponding dimensions, the area of cross-section of any part (such as a section of the muscles of the leg) varies only as the square of the corresponding dimensions. In short, the muscles of a fly carrying this great proportional weight undergo no greater tension than would be exerted by a colossal insect in walking.
[40]. This has been shown to be the case by Michels, who states that each commissure is formed of three parallel bundles of elementary nerve-fibres, which pass continuously from one end of the ventral or nervous cord to the other. “The commissures take their origin neither out of a central punctsubstanz (or marksubstanz), nor from the peripheral ganglion-cells of the several ganglia, but are mere continuations of the longitudinal fibres which decrease posteriorly in thickness, and extend anteriorly through the commissures, forming the œsophageal ring, to the brain.”
[41]. The following extract from Newton’s paper shows, however, that the infra or subœsophageal ganglion, according to Faivre, has the power of coördinating the movements of the body; still, it seems to us that the brain is primarily concerned in the exercise of this power, as the nerves from the subœsophageal ganglion supply only the mouth-parts. “The physiological experiments of Faivre in 1857 (Ann. des Sci. Nat. tom. viii, p. 245), upon the brain of Dyticus in relation to locomotion, are of very considerable interest, showing, as they appear to do, that the power of coördinating the movements of the body is lodged in the infraœsophageal ganglion. And such being the case, both the upper and lower pairs of ganglia ought to be regarded as forming parts of the insect’s brain.”—Quart. Jour. Micr. Sc., 1879, p. 342.
[42]. The arthropod protocerebrum probably represents the annelid brain (supraœsophageal ganglion). The antennal segment (deutocerebrum), with the premandibular (intercalary) segment (tritocerebrum) originally postoral, have, as Lankester suggests, in the Arthropoda moved forward to join the primitive brain. See Wheeler, Journ. Morphology, Boston, viii, p. 112.
[43]. Viallanes’ assertion that the instincts of the horse-flies and dragon-flies are “lower” than those of the locusts, may, it seems to us, well be questioned.