120 SUBDIVISION OF BEETLE TRIBE. 



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

 often forms a case for itself, of bits of 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 5jointed. 



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 



