54 Annals Entomological Society of America [Vol. IX, 



which seems very probable, then the pleural suture probably 

 arose by an infolding of the integument of this plate. In the 

 pleuron of Periplaneta for example, the line which represents 

 the pleural suture is clearly formed by the two external lips of 

 the infolded integument coming together and resting against 

 each other, but the edges or lips do not fuse. On pressing the 

 edges or lips of the fold apart, a large hollow pocket will be seen, 

 at the bottom of which is the apodeme and the pleural arm. 

 The pleural arm is sometimes hollow and usually chitinized. 

 These conditions would be produced by the infolding of the 

 integument of the pleuron, possibly due to muscular stress, 

 possibly from other causes. This is the simplest and most 

 probable explanation. 



Some investigators regard the pleuron as being formed by 

 two sclerites coming together, fusing and the edges rolling inward 

 to form the pleural suture and apodeme. This view seems very 

 improbable. It is complicated and does not account for the 

 single plate representing the pleuron in Eosentomon, Leuctra, 

 etc. Furthermore, two sclerites whose edges meet and fuse are 

 not apt to be plastic enough to permit their being drawn out 

 into a prolongation forming the pleural arm and pocket, but 

 would more probably be firm and resistant. 



Audouin, '24, considered the pleuron as composed of three 

 sclerites, the anterior or episternum, the posterior or epimeron 

 and the peritreme or spiracle bearing sclerite. This terminology 

 is widely accepted (with the exception of peritreme) in general 

 use and there is no valid reason for changing it as some writers 

 have done, since this only leads to confusion. Kirby refers to 

 the epimeron as the pleura. Burmeister thought the pleuron 

 was part of the sternum and others regard it as the basal 

 sclerites of the leg. 



Heymons, '99, in his "Beitrage zur Morphologic und Ent- 

 wichlungsgeschichte der Rhynchoten," pp. 443, in discussing 

 the sclerites of Nepa, was the first to use the term subcoxa and 

 applied it to what he thought was the mesothoracic pleuron, 

 consisting of episternum and epimeron. A study of Nepa shows 

 that Heymons' subcoxa actually consists of the mesothoracic 

 episternum, the precoxal bridge or precoxale (Crampton, '14), 

 and possibly the trochantin. The sclerite in Nepa which 

 Heymons thinks is the metathoracic pleuron, he terms the 

 "pleurite," pp. 376. This sclerite is not the metathoracic 



