COLEOPTERA. I25 



the intervention of a short flexible piece known as the epistorne the upper lip 

 (labrum) is attached. Running along the middle of the under side of the head 

 there is a piece, generally marked off by a line on each side, which in its posterior 

 part is named the gula, and in front the submentum. The submentum sometimes 

 prolonged beyond the margin of the head in the form of a peduncle gives attach- 

 ment to the lower lip (labium), which consists of a basal piece of variable size and 

 form called the mentum, and a terminal part, the ligula. The latter usually bears 

 two lobes (the paraglossae) at its extremity, while from its base, known as the 

 hypoglottis, the labial palpi arise. Between the labrum and labium lie the 

 mandibles and maxillae. The mandibles are strong biting jaws, and are attached 

 to the sides of the head by pivot-like joints, which permit only of lateral move- 

 ments. They are often much larger in the males than in the females, and in the 

 males of some forms such as the stag-beetles, attain monstrous proportions. Each 

 of the maxillae consists typically of a stem, composed of two pieces cardo and stipes 

 with a four-jointed palp attached to the outer and two lobes to the inner side of 

 the free end of the stipes. Except in the larval state, beetles rarely possess those 

 eyes with a single lens which are known as ocelli. The compound eyes, on the 

 other hand, are generally large and well-developed, but vary considerably in form, 

 and in the size and number of their facets. They are often simple in outline, 

 sometimes slightly notched in front and reniform, or the notch may extend more 

 deeply and divide the eye into two distinct lobes. Each eye may even be 

 completely divided into two parts, more or less widely separated from one another ; 

 so that some beetles appear to have four eyes instead of two. This appearance is 

 very strongly marked in certain water-beetles, in which one part of each eye is on 

 the upper, and the other on the under side of the head. The eyes of some beetles 

 look coarse and granular, while in others they appear quite smooth and glassy- 

 looking, owing to the small size and slight convexity of their facets. Among the 

 longicorn beetles, it is generally found that in the nocturnal species the eyes are 

 coarser and more granular than in those species which fly during the day; so that 

 the size of the facets seems to have some relation with the conditions of light 

 depending on the habits of the insects. But this curious fact does not, so far as we 

 know, apply to any other family of beetles. Exceptionally also it is found among 

 beetles that the facets in the upper part of the eye are different in size to those on 

 the lower part. The antennae of beetles are scarcely less important in their 

 functions than the eyes. They are in most cases sensitive to touch, and there is 

 reason to believe that these organs are also the chief seat of the senses of smell 

 and hearing. They appear under a variety of different forms, some of which, 

 while subject to minor modification, are pretty constant throughout certain large 

 groups of beetles, and thus account for the names, Clavicornia, Lamellicornia, etc., 

 given these groups. As a rule the antennae, no matter what their length, are made 

 up of eleven joints or segments ; but this number may be increased, in some cases 

 to thirty or forty (Rhipicera), and even to as many as fifty (in the Longicorn genus 

 Polyarthron), or it may be reduced even to so low a number as two (in Platy- 

 rhopalus). When the joints are more or less cylindrical in form, the antennae may 

 be either filiform, if of nearly uniform thickness throughout, setaceous if they taper 

 towards the extremity, or moniliform if each of the joints is short and bead-like. 



