618 



CLASS IV. ISSECTA. 



the adult unless the 

 eyes represent them.* 

 These will be dealt 

 with under the organs 

 of sense. 



The appendages of the 

 second segment are the 

 antennae. These are 

 usually long, multi-seg- 

 mented processes, but 

 they may be reduced to 

 a few segments, or even 

 to one. They vary very 

 greatly in structure and 

 are of much use in classi- 

 fication (Fig. 370). They 

 often exhibit sexual differ- 

 ences. They are ob- 

 viously of the greatest 

 importance to the insect 

 and act as sense organs,, 

 partly tactile, partly 

 olfactory and partly 

 auditory in nature. 



The appendages of the 

 third segment i f we 

 accept the view, as there is very good reason to do, that an 

 intercalary segment exists between that which bears the an- 

 tennae and that which bears the mandible disappear in the 

 adult except in the primitive family Campodeidae f where 

 they persist as paired tubercles. 



The appendages of the fourth segment are the mandibles. 

 These never bear a palp as they do in most Crustacea (Fig. 371). 

 They may be toothed, stout, unjointed J structures as in biting 

 insects, or they may be modified into sickle-shaped or even 

 tubular piercers as in the larvae of some water beetlss, or they 

 may take the form of piercing, slender blades as in Hemi- 



* v. tables on p. 325 and on p. (509, and the discussion on p. 349. 



f H. Uzel, Zool. Anz., xx, 1897. W. M. Wheeler, J. Morph.,\n\, 1893, p. 1. 



Traces of segments are described in the mandibles of some beetles. 



FIG. 370. Different forms of antennae (after Bur- 

 meister). a Bristle-like antenna of Locustz ; b 

 filiform antenna of Carabus : c moniliforra antenna 

 of Tenebri-) ; d dentate of Elater ; e pectinate 

 antenna of Ctenicera ; / crooked antenna of Apis ; 

 g club-shaped of Silpha ; h knobbed of Xecro- 

 phorus ; i laniellated of Melolontha ; k antenna 

 with bristle from Sargus. 



