596 EXTERNAL ANATOMY OF INSECTS. 



in soft ones they also are soft. The most impenetrable 

 ones that occur to my recollection are those of Illiger's 

 o-enus Doryphora, and the softest and most flexile those 

 of Telephones, Meloe and affinities. With regard to in- 

 dividuals, they are mostly as hard as the prothorax, and 

 harder than the back of the abdomen. Elytra also, as 

 far as my observation goes, are never diaphanous. 



2. Articulation with the trunk. This is by means of 

 a process of the base of the elytrum which I call the axis a 

 or pivot, attached by elastic ligaments, and certain little 

 bony pieces {osselets Chabr.) in the socket under the side 

 of the anterior angle of the dorsolum b . You may easily 

 remove the elytra attached to the mesothorax from Geo- 

 trupes stercorarins, which will enable you to see the mode 

 of articulation with little trouble . 



3. Expansion. It is by means of the bony pieces just 

 mentioned that the organs in question are opened and 

 shut d under the action of the antagonist muscles. In 

 opening for flight the two elytra recede from each other, 

 and are elevated so as not to retain their horizontal po- 

 sition, which would interfere probably with the play of 

 the wings, but form an angle with the body. When they 

 return to a state of rest, the sutures usually meet and 

 coincide longitudinally ; but in some cases when closed, 

 as in Necydalis, &c, they diverge from each other at the 

 apex; and in Meloe, like the Orthoptera, to which that 

 genus approaches, one laps over the other. 



4. Parts. The parts to be considered in an elytrum 

 are the areas, the axis, the suture, the margin, the epi- 



* Plate XXVIII. Fig. 3—5. V" . 



h Chabrier Sur le Vol des Ins. c.i. 439. 



<-' Plate XXVIII, Fig. 10. «■ Chabrier ubi supr, 



