178 NATURAL ARRANGEMENT OF IXSECTS. 



only be those which burrow in sand, and similar con- 

 crete substances, that would require such a brush-like 

 implement. But we subsequently found, that even 

 some truly predaceous sand burrowers (for we caught 

 them with their prey) were unfurnished with this 

 structure. This circumstance strongly proves how un- 

 safe it is to theorise too hastily upon a few facts only. 

 The wood burrowers, however, seem to possess a less 

 variable peculiarity, which is in intimate connection 

 with their economy and habits. They are generally 

 lengthy insects, and have short legs ; but their dis- 

 tinguishing feature is to have either very large and 

 strong mandibles, dilating towards their extremity ; or 

 where these are smaller, not dilated, and parallel, they 

 are then shorter and more compact, and the head is 

 then considerably enlarged, to give room for the exer- 

 cise of powerful muscles. We thus see how provident 

 Nature is of her creatures ; she endows them with 

 peculiar instincts, and, for the exercise of those in- 

 stincts, furnishes them with the requisite instruments. 

 A lengthened body and short legs is not confined to the 

 wood burrowers, for we find it conspicuous in the 

 ScoliadcB, Crahronidce, and Philantliidce. The characters 

 upon which these insects have been collected into 

 families are not sufficiently precise; and very many 

 forms, we have not the least doubt, still remain to be 

 discovered. The Scoliadce and Pompilidce are the only 

 families among them which present a thorax con- 

 structed similarly to that observed in the male Mu- 

 tillidce, and which is more or less developed according \ 

 to the genera, and extends backwards as far as the i 

 insertion of the superior wings. We perceive a modi- 

 fication of this structure in the Ampulicidce, which 

 forms the transition to the collar of the rest of this 

 group. Their eyes are usually lateral and ovate ; but in 

 some they are kidney-shaped, whicli indicates a de- 

 parture to that normal form found in the Vespidcp. In 

 the Scoliadce, Scolia itself exhibits to us the most bulky 

 insects in the group. This genus is of universal distri- 



