366 THE ANATOMY OF INVERTEBRATED ANIMALS. 



gnathites of the type exhibited by the Orthoptera. The 

 absence of palps is a very significant fact, suggesting that 

 the Hemipteran mouth is the extreme term of a series of 

 modifications for the commencement of which we must go 

 back to the Myriapoda. 



The metabolous Coleoptera, or Beetles (Fig. 105), have 

 masticatory mouths of the same general type as those of the^ 

 Orthoptera / with which they are closely connected through 

 the Earwigs. The two constituents of the labium are, how- 

 ever, much more completely confluent than in the Orthoptera. 

 There are usually two pairs of wings, the anterior pair being 

 converted into stiff horny elytra ; these take no part in the 

 act of flight, but serve as covers to the metathoracic wings, 

 which, in the state of rest, are folded up beneath them. The 

 number of apparent somites of the abdomen is often much 

 reduced. In the metabolous JVeuroptera (Ant-lions, Caddis- 

 flies, Scorpion-flies), in some of which the insect is more or 

 less active during the pupa-state, the parts of the mouth are, 

 for the most part, very similar to those of the Orthoptera. 

 In two groups of JVeuroptera, however, the mouth becomes 

 suctorial. Thus, in the Trichoptera, or Caddis-flies, the labrum 

 is elongated and grooved posteriorly ; the mandibles are 

 aborted, the bases of all the gnathites are united, and the 

 labrum is a spoon-shaped body. In the Scorpion-flies (Pa- 

 norpind) there is, according to Gerstfeldt, a proboscis formed 

 in front by the elongated clypeus and labrum, and behind by 

 the coalesced maxillae. The mandibles are small, and the 

 first maxillae much elongated. The ordinary four palps are 

 present. 



The Neuroptera have two pairs of wings of a delicate 

 reticulated structure. The metathoracic wings may or may 

 not be folded. 



What appears to be a further development of this type 

 of mouth is found in the Lepidoptera (Butterflies and Moths). 

 The labrum and the mandibles abort, and the labium is rep- 

 resented only by a triangular plate which bears two large 

 palps. On the other hand, the maxillae, the palps of which 

 are always very small, are often immensely elongated and 

 applied together by their channeled inner faces, thus consti- 

 tuting a sucking proboscis (Figs. 106, 107). The wings, simi- 

 lar in character, and covered with minute scales, are rarely 

 absent. Both pairs are used in flight. 



In the metabolous Diptera (Flies and Fleas, Fig. 108) 



