888 



INSECTA. 



according to the figure by Mr. Curtis',* 

 it is a.broad oval plate, much larger than either 

 of the other parts of the labium. This irre- 

 gularity in its size is very perplexing in examin- 

 ing the parts of the mouth, since in those cases 

 in which it is developed to a great extent the 

 ligula is often so much reduced in size as to 

 appear entirely absent, and to render it a matter 

 of consideration whether it would not be better 

 to consider the palpiger in all cases as only the 

 inferior portion of the true ligula, since, in a 

 great number of instances in which the pal- 

 piger is large, the ligula is very small; and, as 

 in the instance of Cychrus, is formed only of 

 minute linear lobes, situated upon and almost 

 hidden by the palpiger. The ligula (i) is the 

 most anterior portion of the under lip. It va- 

 ries as much in shape and size as the palpiger. 

 In Hydrous it is divided into two lobes by a 

 slight fissure in its anterior margin, which is 

 membranous, and covered, as well as its in- 

 ternal surface, with short smooth hairs. It is 

 the part which properly represents the true lip, 

 its internal surface being continuous with the 

 soft membrane of the mouth. In most of the 

 Geodephaga? it is divided into three linear 

 lobes, not very unlike in their appearance to the 

 true palpi. This division into lobes occurs in 

 most of the predaceous land-beetles. In Ci- 

 cindelida the ligula is very minute, and this is 

 the case also in some of the Stapliylinida. In 

 the predatory water-beetles, as Mr. Newman 

 has observed, the ligula is of considerable size, 

 and this is particularly the case in Hydrous. 



The mandibles (fig. 369, f, fig. 370, A), the 

 true organs of manducation, are two exceed- 

 ingly large and strong arched jaws opposed to 

 each other, and sometimes decussating like the 

 blades of a pair of scissors. This is the case 

 in the most rapacious insects, Cicindelidte, 

 Slaphylinidie, 4'C. In the Hydrous they do 

 not decussate. They are situated immediately 

 beneath the clypeus and labrum on each side, 

 and are connected by a ginglymoid articulation 

 with die upper and under surface of the head. 

 The superior external coiidyle moves in the 

 articulating surface of the small bone (Jig. 

 372, <?), a little anterior to the bone of the 

 antenna (r) and the inferior external condyle 

 (fig. 370, /. 3) in the articulating surface 

 (.fig- 372, y) of the os transverswn. In this 

 insect their form is somewhat like that of 

 a sickle or garden knife. They are thick 

 and strong at their base, and hooked at their 

 apex, and are armed with three projecting, 

 notched, or double-pointed teeth. The inter- 

 nal margin of the apex of the mandible is 

 excavated or grooved, as also are the teeth 

 along their posterior surface. The object of 

 this has reference, probably, to the habit of 

 the insect, the structure of the jaws being 

 somewhat similar in this respect to that of the 

 jaws of the more rapacious Dyticus, which is 

 said to prey upon small fishes and water- 

 insects. The under surface of the internal 

 margin of each mandible is covered with soft 

 villi, and there are four condyles to each 

 mandible. Those just described perform the 



* British Entomology. 



A, mandible ; 1, process for 2, extensor tendon ; 

 3, process to articulate with the inferior surface of 

 the cranium; 4 & 5, flexor tendon; 6, internal 

 margin of jaw; 7, bifid teeth. 



li, under surface of the maxilla. 



C, internal or upper surface; 1, cardo ; 2, 

 stipes ; 3 & 4, palpifer ; 5, lacinia ; 6, galea ; 7, 

 lobus inferior 8, unguis ; 9, retractor maxilla ; 

 10 & 11, levator cardo. 



chief motions ; the others are the middle ex- 

 ternal condyle (1), which gives attachment to 

 the tendon of the great extensor muscle, and is 

 situated between the superior and inferior con- 

 dyles ; and the internal condyle (6) is situated 

 on the internal posterior margin of the man- 

 dible, and gives attachment to the flexor 

 muscles of the jaw. The internal margin of 

 the mandible is also rendered concave, and 

 forms part of the lateral boundary of the epi- 

 pharynx. From the general structure of the 

 mandible we at first are lead to suppose that 

 the habits of the insect are entirely carnivorous, 

 but it is said to subsist chiefly upon aquatic 

 plants, although it feeds with avidity on dead 

 larvae and aquatic mollusca.* In the truly 

 carnivorous Coleoptera, the Cicindelida:, Cara- 

 bidtc, and others, the mandibles are acutely 

 pointed ; but in those which feed upon vege- 

 table matter, leaves of trees, &c., they are 

 thick and obtusely dentated, as in Melolon- 

 thida. In the generality of species the man- 

 dibles are always strong dentated organs, but 

 a few exceptions occur in the Cetoniidie, which 

 feed on the pollen of flowers, and in the 

 Ajihodiadte, which subsist on the recent excre- 

 ment of cattle, in which their margins are soft 

 and flexible. They are always the most con- 

 spicuous parts of the mouth, and differ from 



* Weitwood, Introduct. Entomology, vol. i. p. 



