466 



AN INTRODUCTION TO ENTOMOLOGY 



of beetles. Another recent paper in which the venation of the wings 

 of many beetles is figured is that of Graham ('22). 



Fig. 546. — Tracheation of wing of imago of Calosoma. (From Forbes.) 



4thA, 



3dA, 



Fig. 547. — Tracheation of wing of imago of Dytiscus verticalis. (From Forbes.) 



Beetles undergo a complete metamorphosis. The larvae, which 

 are commonly called grubs, vary greatly in form; some 

 are campodeiform, others are scarabeiform, and some 

 are vermiform. In some members of the order there 

 is a hypermetamorphosis, the successive larval instars 

 representing different types of larvae; this is true of 

 members of the Meloidce and Micromalthidas. Oc- 

 casionally individuals of Tenehrio molitor are found in 

 which the wings are developed externally. The pupae 

 Fig. 548. — Pu- are exarate, that is, the limbs are free (Fig. 548) . These 

 pa of a bee- insects usually transform in rude cocoons made of 

 earth or of bits of wood fastened together by a viscid 

 substance excreted by the larvae. Many wood-burrowing species 

 transform in the tunnels made by the larvae ; and some of the Dermes- 



