XXXU INTRODUCTION. 



universally maintained. In the figures given in this volume these 

 apertures have been portrayed iu nearly every genus. 



The five appendages to the thorax, the two pairs of wings 

 and the thi'ee pairs of legs, must now be described. The anterior 

 wings or hemelytra are the most important, as they are not 

 only very diverse in structure but they also afford taxonomic 

 characters very largely used in the classification of some groups 

 and families. 



The corium is the hard, coriaceous portion, and the clavus 

 a similar but distinctly divided portion l3'ing next to the scutellum. 

 The membrane or apical portion of the hemelytron is nearly always 

 present, though sometimes in a very reduced or aborted condition, 

 and the veins vary very much in number and arrangement ; in fact 

 the variation is so great iu different genera of the same family, as 

 in Pentatomidse, that at present little sound evolutionary guidance 

 seems to be afforded by the venation, unless averages and large 

 groups are studied. The posterior wings need scarcely be con- 

 sidered at length in this place, as they are seldom used as 

 classificatory characters, with the exception of the hamus, some- 

 times present as a spur-like vein to the cell. 



Fig. 5. — Anterior wing or hemelytron of a Capsid. 



a. Clavus. 



b. Corium. 



c. Cuneus. 



d. Membrane. 



e, e. Cells of membrane. 



The corium, however, iu some families possesses an increasing 

 specialization in structure ; thus in the Capsidse a distinct addition 

 may be noticed in the appearance of a cuneus, or separation of the 

 external apical area of the corium. 



Fig. 6. — Anterior wing or hemelytron of a Cimicid. 



a. Clavus, 



b. Corium. 



c. Embolium. 



d. Cuneus. 



c. Membrane. 



In the Cimicidse another division of the corium occurs, and an 

 embolium, or separation of the lateral area of the corium, is. 

 observed. 



