404 



THE INSECTA. 



§326. 



furthermore, from the others, in their transverse striae being less distinct, and 

 their fibrillae being more easily observed; indeed, with most species, these 

 last show a tendency to separate even from the least pressure, while those 

 of the other voluntary muscles are very compactly united together. *-' 



The muscles are attached directly upon the cutaneous skeleton, as with 

 the Crustacea. In the extremities, only, do there appear to be tendons ; 

 but these are merely very long, flattened processes of the skeleton, situated 

 in the axis of the articles of the extremities. They serve as points of 

 attachment to short muscular fasciculi which are there obliquely inserted, 

 after having arisen from the inner surface of the articles. With adult 

 insects, the segments of the body are only slightly movable, and have but 

 few muscles. But with the larvae, whose extremities are rudimentary, or 

 even wholly wanting, there is a very prominent muscular system situated 

 directly beneath the skin, and composed often of several layers of flattened 

 fasciculi. <^^ 



§ 326. 



The Locomotive organs, properly speaking, of the Insecta, are the legs 

 and the wings. The true legs never exceed three pairs, and are inserted 

 upon the first three segments back of the head — Prothorax, Mesothorax, 

 Metathordx. Each leg is divided into a Coxa, a Trochanter, a Feinur, 

 a Tibia, and a Tarsus. The tarsus is divided into several articles, the 

 number of which reaches even five. The form of these legs varies infinitely 

 according to the mode of life of each species. The most common are those 

 to which are usually given the names : Pedes cursorii, arahulatorii, gressorii, 



2 This is so with the Diptera, Hemiptera, and 

 Hymenoptera, with the muscles of whose wings the 

 elements may be very easily separated.* 



3 Lyonet (Traite, &c., p. 114, PI. VI.-VIII.) has 

 given a very detailed account of the muscles of the 

 larva of Cossus. See also Newport, Philos. 

 Transact. 1836, p. 537, PI. XXVII. (the cutaneous 

 muscles of the larva of Sphinx ligustri), and 



Straus, Consid. &c. p. 140, PI. HI. IV. (Melolon- 

 tha vulgaris). 



Reference may be also made to the works of 

 Meckel (System, &c., III. p. 22), Cuvier (Lemons, 

 &c. II. p. 64), Burmeinter (Handb. &c. I. p. 267), 

 Lacordaire (Introduct. d I'Entomol. II. p. 249), 

 and of Newport (Cyclopaed. &c. loc. cit. p. 934). 



* [ § 325, note 2.] The delicate and beautiful 

 structure of the thoracic muscles of some of the In- 

 Becta, lias been carefully studied of late, and has 

 aided not a little in the elucidation of the histology 

 of the muscular tissue. See Lebert, Recherches 

 8ur la formation des muscles, &c., in the Ann. d Sc. 

 Nat. XIII. 1850, p. 182-195, PI. VII. fig. 18-27 ; 

 but especially Aubert, Ueber die eigenthumliche 

 structur der Thoraxmuskeln der Insekten, in Sie- 

 hold and Kollilcer^s Zeitsch. IV. 1853, p. 388. 



This last-mentioned naturalist states that he has 

 observed a new form of muscle-element in the 

 thorax of the Libellulidae, consisting of primitive 

 muscular bands by means of which, with a beaker- 

 shaped apparatus, the wings are moved. These 

 fibres consist of flattened riband-like bands, striated 

 on their borders as well as on their flat surface. 



I have recently studied the elements of the 

 thoracic muscles of many Diptera (jCulex, espec- 



ially) with the highest and best microscopic powers. 

 The discs composing the primitive fibrillae, easily 

 separate and may be studied by themselves. But, 

 with the best powers, I have been unable to observe 

 in them anything but that each disc is a solid, 

 homogeneous light-refracting body. The fibrilla 

 appears to be formed by the aggregation of these 

 discs in a linear series and with regular inter- 

 spaces ; no sheath, by which these discs would be 

 retained in a row, was observed. Contraction of 

 the fibrilla takes place by an approximation of the 

 discs to each other, and the consequent greater or 

 less disappearance of the interspaces. These phe- 

 nomena can be easily observed, and, it may be 

 added, there are often seen isolated fibrillae con- 

 tracting and relaxing, thus showing that the real 

 phenomenon of muscular contraction, does not de- 

 pend upon the nervous system, however much the 

 action of this last may serve as a stimulant. — Eu. 



