682 EXTERNAL ANATOMY OF INSECTS. 



I seem to have observed three kinds of tarsal articula- 

 tion. Thejirst is a species of enarthrosis or ball and socket, 

 the joints terminating in a globular head, perforated in- 

 deed for the transmission of muscles, &c, and which is 

 received by a corresponding cavity of the tibia or pre- 

 ceding joint, as may be seen in many weevils (Curciclio 

 L. a ). This admits of some rotatory motion. — The second 

 is a mixed articulation between enarthrosis and gingly- 

 musy when at the base of the ball a deep transverse 

 channel receives a corresponding ridge of the tibia: or 

 preceding joint : this may be found in Rutela and pro- 

 bably many other Lamellicorn beetles ; and something 

 very similar in the Predaceous ones. — The third kind is 

 where there is little or no inosculation, and the joints are 

 scarcely more than suspended: this takes place in the 

 Orthoptera, Neuroptera, &c. ; but in Blatta and the hind 

 legs of Mantis there is some approach to the foregoing 

 kinds. 



We are now to consider the number of joints of the 

 tarsus, which varies considerably in the different Orders, 

 and in one has been assumed as a clue for a subdivision 

 of it into sections 5 , which, though not perfectly natural, 

 is very convenient, and has been adopted by most modern 

 Entomologists. In treating of this head, I shall use 

 those denominations that have been employed by M. La- 

 treille and others to express the variations of the num- 

 ber of the tarsal joints in the Coleoptera, but shall apply 

 them to insects in general. Insects in this view, there- 

 fore, may be called pentamerous ; heteromerous ; tetra- 

 merous; trimerous ; dimerous ; or monomer ous. 



8 Plate XXVI. Fig. 44, 46, 47. a. 

 b By Gecfl'roy— Hist. Ins. i. 58. 



