THE EYES OF A BEETLE. 



11 



terms ligula and labium are often used synonymously. However, m 

 the descriptions which follow, the term ligula is used to designate 

 the piece in front of the mentum bearing the labial palpi. These 

 palpi are usually 3-jointed (in certain Staphylinids 2- or even 4- 

 jointed). The terminal joint is often of the same form as that of 

 the maxillary palpi, and offers in many cases important characters 

 used in classification. Both mentum and labium form an under lip 

 which prevents the food from falling backwards out of the mouth 

 and, with the aid of the maxillae, pass it forward to be crushed be- 

 tween the mandibles, the two sets of appendages thus acting much 

 as the tongue of vertebrates. 



The Eyes. The eyes of beetles vary greatly in size and shape, 

 and each is composed of a large number of facets or simple lenses 

 in each of which a single filament of the optic nerve ends. These 

 lenses also vary much in size, and the terms "'coarsely granulated" 

 and " finely granulated" are used to denote this variation. In the 

 family Gyrinida? and in the genus Oberea the eyes are wholly di- 

 vided, two being above and two on the lower surface of the head 

 thus enabling the beetle to see upward and downward at the same 

 time. In many species of Cerambycida? and other families they 

 are often deeply notched or emarginate. either in front or on one or 

 the other of the sides. Rarely they are wholly wanting; rarely, 

 also, as in certain Staphylinids. there are one or two simple eyes or 

 single lenses called ocelli located on the back part of the vertex, be- 

 tween the compound ones. 



In the CicindelidcP and many of the Carabida?. the head bears, 

 in addition to the regular pubescence, rather long, erect seta? or 

 bristle-like hairs, which arise from special punctures located above 

 and -close to the inner margin of the eyes. These are known as 

 supraorbital seice. 



The Antenna. The principal appendages attached to the head 

 are the antenna. They vary greatly in form, point of insertion, 

 and number of joints, and these characters are much used in classi- 

 fication. In the true Coleoptera they are inserted in front of or 

 more rarely between the eyes, often under the side margin of the 

 front. In the Rhynchophora they are borne upon some portion of 

 the beak. The number of joints varies from two in Adranes to 25 

 or 27 in Prionus. the usual number being 11. The basal joints are 

 usually less pubescent and of a firmer texture than the outer ones. 

 In the latter the surface is usually more or less covered with minute 

 pores which increase greatly the sensitive area. In those genera m 



