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 isa 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 — Prothorazx, Mesothoraz, 
Metathorax. 
Each leg is divided into a Coxa, a Trochanter,a Femur, 
a Tibia, and a Tarsus. The tarsus is divided into several articles, the 
number of which reaches even five. 
according to the mode of life of each species. 
The form of these legs varies infinitely 
The most common are those 
to which are usually given the names: Pedes cursuri, ambulatorii, 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 (Traité, &c., p. 114, Pl. VI-VIIT.) has 
given # very detailed account of the muscles of the 
larva of Cossus. See also Newport, Philos. 
Transact. 1836, p. 537, Pl. XXVII. (the cutaneous 
muscles of the larva of Sphing ligustri), and 
* [ § 325, note 2.] The delicate and beautiful 
structure of the thoracic muscles of some of the In- 
secta, has been carefully studied of late, and has 
aided not a little in the elucidation of the histology 
of the muscular tissue. See Lebert, Recherches 
sur la formation des muscles, &c., in the Ann. d Se. 
Nat. XIII. 1850, p. 182-195, Pl. VII. fig. 18-27 ; 
but especially Aubert, Ueber die eigenthiimliche 
structur der Thoraxmuskeln der Insekten, in Sie- 
bold and Kélliker’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 (Culex, espec- 
Straus, Consid. &c. p. 140, Pl. III. IV. (Melolon- 
tha vulgaris). 
Reference may be also made to the works of 
Meckel (System, &c., III. p.-22), Cuvier (Legons, 
&c. IL. p. 64), Burmeister (Handb. &c. I. p. 267), 
Lacordaire (Introduct. & ?Entomol. II. p. 249), 
-and of Newport (Cyclopaed. We. loc. cit. p. 984). 
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. Ep. 
