THE INTERLOCKING MECHANISMS WHICH ARE 



FOUND IN CONNECTION WITH THE 



ELYTRA OF COLEOPTERA. 



ROBERT S. BREED and ELSIE F. BALL. 



It is a matter of common knowledge that the elytra of most 

 beetles are co-adapted with each other and with the body of the 

 insect. Yet it appears that no one has ever described these co- 

 adaptations in any detail in spite of the fact that several very in- 

 teresting mechanical devices are here brought into use. The at- 

 tention of the senior author of this paper was called to them while 

 studying the muscular system of beetles. At that time he dis- 

 covered that a small muscle, attached to the meta-episternum, 

 had been erroneously thought to be an expiratory muscle and 

 that in reality it operated a mechanism for hooking the edge of 

 the elytron to the body at this place (Breed, :03, page 332). 



Writings on the subject seem to be limited to a few general 

 statements in text-books. Packard ('98) says that the wing cases 

 of beetles join along their dorsal suture like the valves of a 

 mussel shell. He further states that there is an interlocking of 

 the elytra with the scutellum, citing the stag-beetle as an ex- 

 ample. He also finds that the elytra of stag-beetles interlock 

 with each other by means of a groove, and that this is the method 

 usually found in beetles ; but that in some cases the joining is 

 after the method of two cog-wheels. He likens these devices to 

 the two methods most used by the cabinet-maker in joining 

 boards. 



Sharp ('99) says that in most beetles the elytra are fitted to- 

 gether and to the sides of the body, except at the tip, but he gives 

 no further explanation. He also states that sometimes the tips 

 of the elytra are fastened to the body, but that this occurs only 

 in the cases where the abdomen is not entirely covered by them. 

 He says further that in the blister beetles, which include the 

 Cantharides and the Meloides, the elytra are not co-adapted with 

 the abdomen. The former are winged but the latter are so-called 



