ENTOMOLOGY. 
Ill 
mesothoracic pair is called the anterior, upper, or 
primary wings ; the metathoracic pair, the posterior, 
under, or secondary wings. When a single pair only 
exist, they are attached to the mesothorax, except in 
one recorded instance, the Asckiphasma annulipes, 
which has posterior wings •without the least trace of 
an anterior pair. 
In general form, structure, and relative size, they 
undergo a great variety of modifications in the diffe- 
rent orders ; and it is from these modifications that 
the respective orders derive their names. Sometimes 
all the four are of similar membranous structure, and 
either all equal in size, ( [Neuroptera ,) or the anterior 
pair largest, ( Hymenoptera , &c.) At other times, 
the anterior are rigid and horny throughout their 
whole extent, ( Coleoptera, ) or only on one-half of 
their surface, (Hemiptera Heteroptera.) In some 
instances, ( Orthoptera , &c.) the anterior wings are 
what is called pergameneous — that is, of a substance 
between coriaceous and membranous, or somewhat 
resembling parchment. 
The harder the substance of which wings are com- 
posed, the less active is the share they take in flight. 
When they consist entirely of a hard horny substance, 
(as among the Coleoptera,) they can he subservient 
to this use in a very trifling degree ; their primary 
and important function being to protect the inferior 
wings and the abdomen. They are, accordingly, 
distinguished by a name significant of their use, 
namely, elytra , sheaths or coverings. In proportion 
as the membranous portion of the wing gains upon 
the denser part the wing becomes a more efficient 
