COLEOPTERA. 495 



mesothorax often bear a striking resemblance to elytra (this 

 can be well-seen by removing the scales from the paraptera, 

 orpatagia, as they are termed, of a sphinx moth) ; and the 

 fact that in many Coleoptera {e.g., Dytiscus) what appear to 

 be rudiments of the fore wings exist beneath the elytra. 



The argument based on the thickened structure of the 

 elytra loses its force when we consider the more or less elytra- 

 like wings of many other insects (Heteroptera, certain Blatti- 

 dae, et al.) ; and it probably would not have been seriously 

 urged but for the presence of the so-called rudimentary wings 

 beneath the elytra of certain beetles. These, however, have 

 been found to correspond in structure and position to the 

 alulae of the wings of other insects; but most important of 

 all, a study of the development of elytra has proven that they 

 are wings. 



The hind wings are membranous, and in most species very 

 efficient organs of flight. But in some of the pre-eminently 

 running beetles the hind wings are wanting, and the elytra 

 serve only as a protection to the abdomen. With some of 

 these insects the elytra are even grown together where they 

 meet on the middle line of the back. Instances of this kind 

 are not uncommon among the ground-beetles and the dark- 

 ling beetles. 



The different mouth-parts are very evenly developed ; 

 we do not find some of them greatly enlarged at the ex- 

 pense of others, as in several other orders of insects. The 

 upper lip, or labrum, is usually distinct ; the mandibles are 

 powerful jaws fitted either for seizing prey or for gnawing; 

 the maxillae are also well developed and are quite compli- 

 cated, consisting of several distinct pieces; the maxillary 

 palpi are usually prominent ; and the lower lip, or labium, is 

 also well developed and complicated, consisting of several 

 parts and bearing prominent labial palpi. 



The larvae are commonly called grubs. They are usually 

 furnished with six thoracic legs, and often with a single 

 proleg at the caudal end of the body ; some, however, as 



