$ 326. THE INSECTA. 405 
natatorit, saltatorii, raptorii, and fossorii.Y The tarsal articles are often 
enlarged, in which case they form, on their under surface, either a naked, 
fleshy sole, or a thickly-pilose ball of the foot, which is usually cordiform. 
With the Dytiscidae, several of these tarsal joints are changed into a disc 
provided with suckers. The last article of these organs bears usually two 
movable hooks, which are sometimes deeply bifid or denticulate on their con- 
eave border.” Itisrare that there isa third hook between them.” But with 
the Strepsiptera, and Physopoda, all the hooks are wanting. The Diptera 
and many Hymenoptera, have, moreover, under these hooks, soft lobules 
(Arolia) provided with numerous small papillae, by means of which these 
insects can fix themselves to objects. With a great number of larvae, the 
six legs are very short or abortive, or even completely wanting. In the 
dirst case, they consist, usually, of merely a hook, but these larvae have also 
many short obtuse processes on the other segments of the body, and by 
means of the hairy soles on the extremity of these, they can fix themselves 
on bodies and thereby move along. With many entirely apodal larvae, 
these processes are replaced by simple tubercles, or by belts of backwardly- 
pointing bristles or spines, which serve as points of support in their loco- 
anotion.® 
The organs of flying are the anterior and the posterior Wings. The first 
are inserted on the mesothorax, and the second on the metathorax ; but in 
nearly all the orders, there are genera with which these organs are wholly 
wanting.” In other genera, the females alone are wingless,® which is 
also true of the neuters of certain families.” It is more common still, to 
see the posterior wings changed into balancers ;“” and this same transforma- 
tion occurs also, but very rarely, with the elytra.™ The wings, properly 
speaking, are only prolongations of the cutaneous skeleton traversed by 
tracheae and blood-canals. Their forms, their nervures, their folds, &c., as 
well as their sometimes complete abortive condition, may here be passed 
over, for all these points belong to the domain of Zoology.* 
1 For the marching, leaping, and swimming of 
insects, see Straus, Considér. &c. p. 180. 
2 Thus, the hooks are bifid with Medoe, and den- 
ticulate with the Pompilidae, Hippoboscidae, Cis- 
telidae, and with Daphnia, Dolichus, Calathus, 
and Pristonychus, of the bid a 
3 This third hook is found, for example, with 
Lucanus cervus. With larvae of the Meloidae, 
the legs are terminated by three very remarkable, 
straight, lanceolate hooks, known by the name of 
Triungulinus. Many of the Curculionidae can 
grapple objects by means of the immovable hooks on 
their tibiae. y 
4 The Tenthredinidae have a lobule of this kind 
on each of their legs, and the Diptera have even 
two to three. For these lobules, as well as for the 
tarsi of Insecta in general, see the beautiful figures 
given by Everard Home Mares on Comp. Anat. 
IV. Pl. LXXXI.-LXXXJV.). According to Black- 
wall (Trans. of the Linn. Soc. XVI. p. 487, 767 3 
and Ann. of Nat. Hist. XV. p. 115), the papillae of 
the Arolia secrete a viscid substance which en- 
ables the Insecta having these organs to walk on 
* (§ 826.] Leidy (Proceed. Acad. Sc. Philad. 
III. 1846, p. 104) has described a peculiar mechan- 
ism by which the membranous wings of Locusta 
are closed in a plicated manner like a fan. This 
mechani ists of spiral lig t bands, 
wound, like the thread of a screw, around the 
transverse or connecting veins, which latter are 
also flexible. By this arrangement, upon the con- | 
steep and smooth surfaces. But this assertion re- 
quires further proof, although it is admitted by 
Spence (Trans. of the Entomol. Soc. IV. p. 18). 
5 With the Lepidoptera, and Tenthredinidae. 
6 With many Diptera. 
7 Among the Orthoptera, the wings are wanting 
with some Blattidae, Acrididae, Phasmidae, and 
Psocidae ; among the Hemiptera, with Acanthias, 
and Rhizobius; and among the Diptera} with 
Melophagus, Phthiridium, and Pulex flagel- 
los. 
8 With Lampyris, some Blattidae, Coccidae, 
Bombycidae, Geometridae, also with the Mutillidae 
and the Strepsiptera. 
9 With the Formicidae and the Termitidae. 
10 With the Coccidae and the Diptera. The pos- 
terior wings are entirely wanting with some Ephem- 
eridae. 
11 Tke two singularly distorted balancers of the 
Strepsiptera, situated in front of the wings and in 
rapid and unceasing motion, are, from their inser- 
tion, only abortive elytra. 
traction of the alary extensors, the spring-like liga- 
ments, or ligamenta spiralia, are stretched in the 
expansion of the wings, and upon the relaxation or 
cessation of the act.on of the muscles, the physical 
properties alone of the ligamenta spiralia, in re- 
Buming their unstretched state, close the wings. — 
Ep. 
