Fig. 235.—Striated muscular fibre of Hydrophilus: A and B, two fibrillæ in a state of extension; a, thick disk; b, thin disk; c, intermediate space. C, D, portion of the same fibrillæ seen by moving the objective farther away and using a small diaphragm; n, thick; c, thin disk. × 2000 diam.—After Ranvier, from Perrier. E after Gehuchten, from Lang.
In describing the minute structure of the muscles of ants, wasps, and bees, C. Janet states that each consists of a group of fibres diverging from a tendon, which is an integumentary invagination (Fig. 236). Each fibre may be regarded as a multinucleate cell; the sarcolemma represents the cell-membrane. It forms a resistant and extremely elastic tube. The longitudinal (Fig. 236, E) and radiating filaments or reticulum (spongioplasm of Gehuchten) lie in a nutritive filling substance (the hyaloplasm of Gehuchten). The radiating filaments are formed of an exceedingly elastic substance, and serve to sustain the longitudinal filaments, to transmit the nervous stimulus to them, and to bring them back into position after contraction. Janet’s account agrees on the whole with that of Gehuchten.
Fig. 236.—Preparations from the adductor muscle of the mandible of Vespa crabro, worker, fixed by heat and alcohol several hours after leaving its cell. A to E × 425; F × 212: A, terminal cupule of the tendon of a fibre. B, C, union of the fibres with their tendon. D, branch of the tendon of a muscle sending out tendons of some of the fibres; this branch is accompanied with numerous nervous ramifications (N). E, fragment of a nerve which furnishes the ramifications of Fig. D. F, fragment of the tendon of the adductor muscle of the mandible; at the left are seen the terminal cupules of the fibres (td, c); on the right, on the body of the tendons, some sessile cupules, each of which forms the attachment of a fibre; td, b, tendons of the fibres.—After Janet.
The muscles of flight are said to be penetrated by fine tracheal branches, probably to supply a greater amount of oxygen, as the most energetic movements of the insect are made in moving the wings during flight; while the other muscles of the body are only surrounded by the air-tubes. (Sharp.)
Without entering into tedious details, the reader is referred to figures or references to the more important systems of muscles, such as those of the legs and other appendages, of the wings, of respiration, etc., to the sections treating of those organs or functions; also to Figs. 16, 17, 18, 22, 48, 74, 81, 83, 84, 115, 116, 172, 173, 174, etc.
Muscular power of insects.—The most detailed and careful experiments are those of Plateau. His experiments prove that even the weakest insects pull at least five times their own weight; many of them, however, get the better of a burden twelve to twenty fold as heavy as themselves, while a strong man or a draught horse, for example, is not even able to pull a burden which is equal to the weight of his body. Plateau came to the following results as to the relation of the weight of the body to the load drawn (1 and 2 are to be compared with each other, 1 being the larger, and 2 the smaller insect; it will be seen that the smaller insect is the stronger).
Fig. 237.—Vespa crabro, worker, fixed by heat and alcohol some hours after leaving its cell. A × 425; B to D × 850 times: A, muscular fibre of the motor muscles of the mandibles treated, for ten minutes, by 1 per cent potassium to bring out the reticulum; the nodes of union of the rayed filaments with the longitudinal filaments are indicated by distinct granulations (l.d), and these longitudinal filaments present accessory thickenings (d.a); T, trachea; N, junction of a nervous filament with the muscular fibres. B, fibre of the same muscle, not treated with potassium, stained by hæmatoxylin; C, transverse section of a disk at the level of a layer of rayed filaments; Sarc, sarcolemma. D, transverse section of a disk at the level of the rods; nuc, nucleus.—After Janet.