INSECTS AND ARACHNIDA. 



243 



the Notonecta (water-boatman) and the Nepa (water-scorpion) are well- 

 known examples, the wings are beautifully variegated by differences in 

 the depth of that hue. The halteres of the Diptera, which are the 

 representatives of the posterior wings, have been shown by Dr. J. B. 

 Hicks to present a very curious structure, which is found also in the 

 elytra of Coleoptera and in many other situations; consisting in a multi- 

 tude of vesicular projections of the superficial membrane, to each of 

 which there proceeds a nervous filament, that comes to it through an 

 aperture in the tegumentary wall on which it is seated. Various con- 

 siderations are stated by Dr. Hicks, which lead him to the belief that 

 this apparatus, when developed in the neighborhood of the spiracles or 

 breathing-pores, essentially ministers to the sense of smell, whilst, when 

 developed upon the palpi and other organs in the neighborhood of the 

 mouth, it ministers to the sense of taste. 1 



640. Feet. Although the feet of Insects are formed pretty much on 

 one general plan, yet that plan is subject to considerable modifications, 

 in accordance with the habits of life of different species. The entire 

 limb usually consists of five divisions, namely the coxa or hip, the tro- 

 chanter, the femur or thigh, the tibia 



or shank, and the tarsus or foot; FIG. 435. 



and this last part is made up of 

 several successive joints. The typical 

 number of these joints seems to be 

 five; but that number is subject to 

 reduction; and the vast order Cole- 

 optera is subdivided into primary 

 groups, according as the tarsus con- 

 sists of five, four, or three segments. 

 The last joint of the tarsus is usually 

 furnished with a pair of strong 

 hooks or claws (Figs. 435, 436); and 

 these are often serrated (that is, fur- 

 nished with saw-like teeth), especially 

 near the base. The under-surface 

 of the other joints is frequently 

 beset with tufts of hairs, which are 

 arranged in various modes, sometimes Foot of Fly. 



forming a complete 'sole;' this is 



especially the case in the family Curculionidce; so that a pair of the feet 

 of the ' diamond-bettle/ mounted so that one shows the upper surface 

 made resplendent by its jewel-like scales, and the other the hairy cushion 

 beneath, is a very interesting object. In many Insects, especially of the 

 Fly kind, the foot is furnished with a pair of membranous expansions 

 termed pulvilli (Fig. 435); and these are beset with numerous hairs, each 

 of which has a minute disk at its extremity. This structure is evidently 

 connected with the power which these Insects possess of walking over 

 smooth surfaces in opposition to the force of gravity; yet there is still 

 considerable uncertainty as to the precise mode in which it ministers to 



1 See his Memoir 'On a new Organ in Insects,' in "Journal of Linnsean 

 Society," Vol. i. (1856), p. 136; his ' Further Remarks on the Organs found on the 

 bases of the Halteres and Wings of Insects,' in " Trans, of the Linn. Society," 

 Vol. xxii. , p. 141 ; and his Memoir ' On certain Sensory Organs in Insects, hitherto 

 undescribed,' in "Trans of Linn. Soc.," Vol. xxiii., p. 189. 



