2 so MANUAL OF ZOOLOGY. 



become hardened Ijy the deposition of chitine, so as to form 

 two protective cases for the hinder membranous wings. In 

 this condition the anterior wings are known as the " elytra," or 

 'wing-cases." In some of the Jfemiptera this change only 

 affects the inner portions of the anterior wings, the apices of 

 which remain membranous, and to these the term "hemelytra" 

 is applied. In the Diptera the posterior pair of wings are 

 rudimentary, and are converted into two capitate filaments, 

 called "halteres," or "balancers." In the Strepsiptera the 

 anterior pair of wings are rudimentary, and are converted into 

 twisted filaments. 



The primitive number of somites in the abdomen of insects 

 is said to be eleven (Orthopterd), but nine is the number ordi- 

 narily present ; and though these are distinct in most laryse, it is 

 seldom that more than seven or eight are recognisable in the 

 adult. The abdominal somites are usually more or less freely 

 movable upon one another, and never carry locomotive limbs. 

 The extremity of the abdomen is, however, not infrequently 

 furnished with appendages, which are connected with the 

 generative function, and not infrequently serve as offensive 

 and defensive weapons. Of this nature are the ovipositors of 

 Ichneumons and other Insects, and the sting of Bees and 

 Wasps. In the Earwig {Forficula) these caudal appendages 

 form a pair of forceps ; whilst in many Insects they are in the 

 form of bristles, by which powerful leaps can be effected, as is 

 seen in the Springtails {Podurm). In some insects (as the 

 Mole-cricket and Cockroach), the 9th or loth abdominal seg- 

 ment carries jointed antenniform appendages, which, though 

 perhaps partially or even primarily generative in function, are 

 certainly organs of sense, being connected with smell or 

 hearing. 



The organs about the mouth in Insects are collectively 

 termed the " trophi," or " instrumenta cibaria." Two principal 

 types require consideration — namely, the masticatory and the 

 suctorial — both types being sometimes modified, and occasion- 

 ally combined. 



In the Masticatory Insects, such as the Beetles (fig. 84, i), 

 the trophi consist of the following parts, from before back- 

 wards : — (i.) An upper lip, or "labrum," attached below the 

 front of the head. (2.) A pair of biting-jaws, or " mandibles." 

 (3.) A pair of chewing-jaws, or "maxillae," provided with one 

 or more pairs of "maxillary palps," or sensory and tactile 

 filaments. (4.) A lower lip, or "labium," composed of a 

 second coalescent pair of maxilte, and also bearing a pair of 

 palpi, the " labial palps." The primitive form of the labium, 



