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). 



Sc R, 



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



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 Meloidee and Micromalthidae. Oc- 

 casionally individuals of Tenebrio 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- 



