932 



INSECTA. 



mary divisions of the leg, connected together 

 by distinct articulations, and in the most de- 

 veloped condition of the limb are almost in- 

 variably found in every insect. The articu- 

 lation of the coxa with the acetabulum is 

 either ginglymoid, as in the Lamellicornes and 

 many others, or cotyloid, as in most of the 

 Rhinchophora ; that between the coxa and 

 trochanter, and between the trochanter and 

 femur, is chiefly of the former kind, which 

 also invariably exists between the femur and 

 tibia, while the articulations of the different 

 joints of the tarsus with one another, and also 

 with the tibia, are almost invariably cotyloid, 

 as in Lucanus, except in the four posterior legs 

 of the Hydradephaga and other water insects, 

 in which they are usually ginglymoid, because 

 the tarsi of these insects being used chiefly for 

 one purpose, that of swimming, this form of 

 joint appears to be necessary to give greater 

 strength to the tarsus, which is employed to 

 strike the water almost wholly in one direction. 



Although the number of joints in the tarsus 

 varies in different insects, it is very constant in 

 some families, which are also connected by 

 other circumstances. Thus in a large group of 

 the Coleoptera the tarsi are invariably com- 

 posed of five joints, besides a terminal claw, 

 and upon this character they have been formed 

 into one group, the Pentamera ; while in 

 another, the Heteromera, there are constantly 

 five joints in each tarsus of the pro and meso- 

 thoracic legs, but only four in each of the two 

 metathoracic. This tendency to the production 

 of the full number of joints is remarkably 

 shewn in many instances. Thus in a large 

 number of families, Psevdo-tetramera, in which 

 on a cursory examination there appear to be 

 only four joints in each tarsus, it is found on a 

 closer inspection that a fifth joint actually does 

 exist, in the form of a very minute articulation 

 (Jig. 398, A, 4), at the base of the terminal 

 joint in each tarsus. So again in another group, 

 Pseudu-trimera, in which there appear at first 

 to be only three joints in each, it is found that 

 there are actually four (B, 3), the additional 

 joint being, as in the preceding instances, de- 

 veloped at the base of the terminal one, but 

 more distinctly than in the Pseudo-tetramera. 

 This tendency to a reproduction of parts is 

 also shewn in the claws at the extremity of the 

 tarsi. In many Coleoptera, as in the Melolon- 

 thid<e (C), each claw is double; while in 

 others, as in Lucanus, in which the proper 

 claw is simple, and articulated to the terminal 

 joint of the tarsus, there is also an unguicula 

 or little claw, supported upon a distinct joint, 

 which is articulated separately from the proper 

 claw, with the last joint of the tarsus, in the 

 middle line below the larger one. 



The variations that occur in the form of the 

 parts of the leg, as in other parts of the body, 

 are directly referable to the habits or necessi- 

 ties of the insect. Thus where the legs are 

 employed chiefly in running, as in the Ci- 

 cindelidae, Carabidte, Scuritidd', and HciJ-palidte, 

 they are usually long and slender, particularly 

 the tarsi and tibia? ; the coxae are very freely 

 articulated with the body, and the trochanters, 



particularly those of the hinder pair of legs, 

 are remarkably large. But when, as in the 

 Gyrinid&f Dyticidae, and Hydrophilidte, they 

 are employed entirely in swimming, they are 

 long, as in running insects, and the tarsi of the 

 second and third pairs are flattened and broad 

 like oars, and their margins, apparently to in- 

 crease the breadth of their oar-like form in the 

 water, without the inconvenience of an actual 

 enlargement of the limbs, are densely clothed 

 with long stiff hairs (K). Besides this, the 

 posterior pair, on which the chief action of 

 swimming depends, are much longer than the 

 others, and the tarsi are ciliated to the very 

 articulation of the unguis. The extremity of 

 each tibia is also armed with one or more long 

 spines, which may assist the insect perhaps in 

 burrowing into the mud. When the legs are 

 employed simply in walking, and the motions 

 of the insect are slow, the legs are all of the 

 same length, and, as in the Chrysomelida, are 

 often covered on the under surface of the 

 tarsi with little hairy cushions, pulvilli. These 

 are generally present also in climbing insects. 

 In the common house-fly, and others of the 

 same genus, instead of hairy cushions the ter- 

 minal joint of each tarsus is furnished near 

 its extremity with two funnel-shaped mem- 

 branous suckers (E), by means of which the 

 insect is enabled to adhere to smooth surfaces, 

 and suspend itself in an inverted position. 

 Each of these is concave, and covered by a 

 membrane, and the manner in which the in- 

 sect attaches itself is by exhausting the air 

 beneath each sucker. The cushions are parti- 

 cularly large in those anomalous insects the 

 Streps iptera, in which they form a broad heart- 

 shaped surface to each joint of the tarsi (M). 

 They are also present, but in a less perfect 

 form, in some of the running insects, the Cicin- 

 delid<K and Carabute, as in Diorycke torta* 

 (MAc'L.), in which the joints of the anterior 

 tarsi are furnished with a little hairy cushion. 

 But in these families the tarsi of the anterior 

 legs of the males are always enlarged for the 

 same purpose as in the Dyticida, that of more 

 securely attaching themselves to the female. 

 This is also the case in Hydrous, in which the 

 terminal joints of the anterior tarsi (fig- 330, A) 

 are very much dilated. In the Dyticid/e 

 the first three joints of the anterior tarsi are 

 consolidated together, and form a broad cir- 

 cular disc, covered with many minute funnel- 

 shaped suckers, two or three of which are 

 much larger than the others; in some, as in 

 Hyderodes Shuckardi, HoFE,t a New-Holland 

 species (H), all the suckers are of nearly the 

 same size. They exist also in the first three 

 joints of the second pair of tarsi (I). A some- 

 what similar structure exists in the males of 

 some of the sand-wasps, Crabronida (F). It is 

 supposed to be designed for the same purpose 

 as in the DyticidoE. But in those insects it 

 consists of a broad and slightly convex dila- 

 tation of the anterior tibiae, and not of the 



* Coleoptevist's Manual, Part ii. tab. 2. 

 4, d. 



t Op. cit. pi. 3, fig. 5. a. b. 



fig. 



