638 



ZOOLOGY 



SECT. 



an additional pair — the so-called maxillula; — occur between the 

 mandibles and first maxillae. In a few eyes are absent. Most 

 have large compound or faceted eyes, and many have simple eyes 

 or ocelli as well ; in a few groups the latter are alone present. 

 The antenna? vary in shape in different groups and sometimes 

 even in the sexes of the same species. They may be tapering, 

 moniliform, club-shaped, pectinate, or plume-like. In addition to 

 functioning as tactile appendages they bear the olfactory setae, and 

 there seems reason to believe that they act also as organs con- 

 cerned in the maintenance of the equilibrium of the body. The 



A & 



uuc, 



Fig. 517.— Mouth parts of the Diptera. 'A, of Tahanus ; B, of Culex. Lettering as in pre- 

 ceding figure : py. hypopharynx ; oc. ocellus. (From Lang.) 



mandibles are always one-jointed, and differ from those of the 

 Crustacea in never being provided with a palp. An arrangement 

 of the mouth-parts adapted for biting or chewing has already been 

 described in the case of the Cockroach : this type is characteristic of 

 the order Orthoptera, to which the Cockroach belongs, and a very 

 similar type characterises the Coleoptera. In theHymenoptera(Fig. 

 516) the mouth-parts are adapted both for biting and for licking 

 and sucking ; the mandibles (ind.) and maxillae (mx 1 .) are sharp and 

 lancet-like, the middle part of the labium is produced into a long 

 median tongue {ligula, li.) at the sides of which are a pair of 

 accessory tongues or paraglossce (prg.). In the Hemiptera there 

 is a proboscis formed from the labium and enclosing the stylet-like 



