THE BEETLES 3089 



the intervention of a short flexible piece known as the epistome 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 some- 

 times prolonged beyond the margin of the head in the form of a peduncle gives 

 attachment 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 mandi- 

 bles 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 movements. 

 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. ]ach 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 generelly 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 in- 

 sects. 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, L,amellicornia, etc., given these groups. As a rule, the antennae, no 

 matter what their length, are made up of eleven joints or segments; but this num- 

 ber may be increased, in some cases to thirty or forty (Rhipicer&)> 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 Platyrhopalus} . When the joints are more or less 

 cylindrical in form, the antennae may be either filiform, if of nearly uniform thick- 

 ness throughout, setaceous if they taper toward the extremity, or moniliform if 

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