120 SUBDIVISION OF BEETLE TRIBE. 



of the abdomen. Previously to undergoing its change, the larva 

 often forms a case for itself, of bits )f earth, or chips of wood, 

 united by silken threads, or by gluey matter. The pupa> or 

 chrysalis, is inactive, sometimes even for years, and takes no 

 nourishment ; but the form of the future Beetle is plainly 

 perceived, the different parts being encased in distinct sheaths. 

 (Fig. 335). 



642. There is much difficulty in forming a simple natural 

 classification of this immense tribe, on account of the great num- 

 ber of distinct species which it includes, and their strong general 

 resemblance to each other. Hence it is often necessary to resort 

 to characters of great minuteness as the ground-work of the 

 system ; and it sometimes happens that, by the adoption of such 

 a plan, tribes which are in reality closely allied in general struc- 

 ture, are placed in different groups, whilst others are brought 

 together which are in many respects dissimilar. No better 

 system, however, has yet been proposed than that of Latreille ; 

 who took as the basis of his classification the number of joints 

 in the tarsus or last portion of the foot ( 607). The four 

 following sections are thus formed. 



I. PENTAMERA (five-parted), in which the tarsi of all the 

 feet are distinctly 5-jointed. 



II. HETEROMERA (differently-parted), in which the tarsi of 

 the first two pairs of feet are 5-jointed, and the two posterior 

 4-jointed. 



III. TETRAMERA (four-parted), in which all the tarsi appear 

 to be 4-jointed. (It has lately been observed, however, that the 

 fifth joint exists in these, although it is very minute, and con- 

 cealed in one of the others.) 



IV. TRIMERA (three-parted), in which all the tarsi have 

 three distinct joints. (A fourth of small size, however, is also 

 present.) 



Each of these sections contains several families ; of which the 

 most important will now be noticed. 



643. Section I. PENTAMERA. The first family of this 

 section consists of Beetles which are exclusively carnivorous ; 

 hunting after, and devouring, other insects; and being carnivorous 



