EXTERNAL ANATOMY OF INSECTS. 67S 



than the thighs, and longer and thicker than the tarsi. 

 Various exceptions, however, to this rule in all these cases 

 might be produced ; but I shall only observe that in all 

 those insects in which the fore-legs are calculated for dig- 

 ging or seizing their prey, as in the Petalocerous beetles, 

 the Gryllotalpa, Mantis, &c, this joint of the leg is 

 usually much enlarged and more conspicuous than the 

 others. 



As to its Jlgure and shape — most commonly the tibia 

 grows thicker from the base to the apex, as in the majority 

 of Coleoptera, Hymenoptera, &c. ; in the Orthoptera, Neu- 

 roptera, &c, it is generally equally thick every where. 

 Another peculiarity relating to this head observable in 

 it, is its tendency to a trigonal figure : this, however, 

 though very general, is not universal ; — thus, in some 

 Orthoptera, as Pterophylla K., its horizontal section is 

 quadrangular; in others, as Locusta Leach and many 

 other insects, it is nearly a circle ; in some scorpions it 

 is almost a hexagon. The superficial shape also of this 

 joint in numerous instances is more or less triangu- 

 lar, but it sometimes recedes from this form : — thus, in 

 Callichroma latipes it is a segment of a circle ; in some 

 Empides it is clavate ; in Onitis Sphinx, dolabriform ; in 

 the Orthoptera, Neuroptcra, &c, it is usually linear ; in 

 some Lygcei it is angular 3 : but the most remarkable 

 tibia in this respect are those of such species of this last 

 genus as have the posterior ones winged or foliaceous, 

 so that they resemble the leaf of some plant — the tibia 

 being the rachis, and the wing (which in some species 

 is veined) representing the leaf itself. This structure is 



» Stoll Punnkcs, I. x.f. 67. t.xvlf. 114. 

 VOL. in. 2 X 



