EXTERNAL ANATOMY OF THE COLEOPTERA. 



these wings are membranaceous, often very large, and 

 lie in a small compass under the elytra when not required 

 for flight, the membrane being thickened where contact 

 takes place on the wing being folded. 



The metasternum (Fig. 10) is usually composed of the 

 sternum (a), the episterna 

 (b b), and the epimera ; but 

 in Dytiscus (and some Geode- 

 phaga) the latter are want- 

 ing, being replaced by the 

 largely developed CQX& (d d) 

 of the hinder legs, of one of 

 which e is the trochanter. 

 The parapleura, or paraptera 

 (c c}, are side-pieces, which 

 in some beetles are very con- 

 spicuous. 



The remaining part is the 

 abdomen, the upper side of 

 which, being covered by the 

 elytra, is softer than the lower, 

 or ventral surface ; the apical 

 segments on the upper side, 

 however, where not covered 

 by the wing-cases, are much harder than the protected 

 portion of the abdomen, and are called the pygidium. 

 The entire abdomen is divided into rings or segments, 

 fitting like those of a telescope, and usually nine in 

 number: in Fig. 11 only six are visible, the extreme 

 apical one, comprising the generative organs, being re- 

 tracted within the sixth (which, in the male, is usually 

 notched, or otherwise altered in outline and surface), 

 and the remainder being only seen on the upper side. The 



Fig. 10. 



Metasternum of thorax of 

 D. marginalis. 



