INSECTA. 



Fig. 369. 



External superior and inferior mtrface of the head of 



Hydrous piceus. 



A r antenna ; a, occiput ; b, epicranium ; c, ocn- 

 li j d, clypeus anterior ; e, labrum ; f, mandibles ; 

 g, maxilla; h, its palpus; t, ligula; k, labial pal- 

 pus;' I, mentum; m, submentum ; n, gula; 0, man- 

 dibnlar ridge. 



trupida, its existence is indicated by a slightly 

 elevated ridge. This suture divides the epi- 

 cranium from the posterior portion of the cly- 

 peus (d), the most conspicuous portion of the 

 head. The proper boundaries of this part 

 have been ascertained with tolerable precision 

 in Coleoptera, but do not appear to have been 

 traced correctly in some of the other orders, 

 particularly in Orthoptera. The clypeus or 

 shield, in Coleoptera, is that broad cover of the 

 anterior surface of the head, bounded poste- 

 riorly by the epicranium and anteriorly by the 

 labrum, with which it is freely articulated. It 

 is the part called by Mr. Kirby the nose, and 

 by Straus Durckheim chaperon. It appears 

 originally to be formed of two portions, which 

 we have called clypeus anterior and posterior, 

 and which are completely united in some fami- 

 lies, as in the Lamellicornes, without trace of 

 their previous distinction, but in others with 

 slight traces of their former separation, as in 

 Hydrous, while both parts are distinctly articu- 

 lated in some of the Dyticida, in which its ante- 

 rior portion appears to be moveable, and has pro- 

 bably been mistaken for the whole clypeus, as 

 has been the case in Orthoptera.* In some 

 species the shield is curiously excavated, tuber- 

 culated, or armed with a long horn, as in Copris, 

 Tyvh*us, and Dynastes, (Jig. 333,) or is minute 



* Newman, p. 9. 



and inconspicuous as in the Cantharida. The 

 original division of the shield into two por- 

 tions in Hydrous appears to be indicated by 

 two rough excavations situated between the 

 triangular suture, its posterior boundary, and 

 the anterior lip. The labrum or upper lip (e) 

 is the most anterior portion of the upper sur- 

 face of the head, bounded only on its posterior 

 margin by the clypeus. It is usually a narrow 

 transverse piece which has been confounded by 

 some writers, particularly by Fabricius, with 

 the clypeus. In some families, Scarabaida 

 and Lucanidte, it is very minute, but, as re- 

 marked by Mr. Newman,* cannot be consi- 

 dered to be in any case entirely wanting, a 

 was supposed by Olivier. In those cases in 

 which it appears to be absent it is concealed 

 beneath a largely developed clypeus. In many 

 families it is large and projecting, and often 

 notched, as in the Carabida and Silphida. It 

 is also very distinct in the water-beetles. It 

 forms the anterior boundary of the mouth. 



The cornea constitute a great portion of the 

 fixed parts of the head. The principal of these 

 (c), the corneae of the true or compound eyes, 

 are situated on the lateral external surfece of 

 the cranium, bounding the basilar piece below, 

 and the epicranium above. They are two large 

 convex surfaces, generally of a nearly circular, 

 but sometimes of a kidney-shaped form, divided 

 into a great number of very minute facets, per- 

 fectly distinct from each other, each of which is 

 the proper cornea of a distinct eye. They are 

 more or less numerous in different insects, 

 amounting in some to no more than fifty in each 

 compound eye, but in others to so many as 

 thirty-six thousand. Thus Lyonet reckoned 

 eleven thousand three hundred in the eye of the 

 goat-moth, and Geoffrey more than thirty-six 

 thousand six hundred in the eye of a butterfly. 

 Each compound cornea is usually situated im- 

 mediately behind the external angles of the 

 triangular or epicranial suture, and is more or 

 less protuberant in different species, as in 

 Hydrous and its affinities. This is particularly 

 the case in the ground-beetles, as noticed by 

 Dalman,t especially in those which reside near 

 water or in sandy situations, as the Cicindelida, 

 &c.; and, as remarked by Mr. Westwood, 

 these protuberant eyes occur mostly in insects 

 of rapacious habits. But it roust further be 

 observed that they occur also in insects which 

 are not of rapacious habits, but require for 

 some other purpose an extended field of vision. 

 This is the case with the males of many species, 

 and most remarkably so in the male of Lampy- 

 ris noctilucctythe common glow-worm, in which 

 the cornea cover almost the whole lateral and 

 under surface of the head. This insect is well 

 known to be attracted by the light of the female. 

 The like occurs in the male of the hive-bee, 

 and in that of some Diptera, as in the Empida, 

 which seek their females, and are constantly 

 found in copula connexos on the wing in the 

 open air. Again, in the sun-beetles, Cetcniida, 



* Paper on the Nomenclature of the Parts of the 

 Head in Insects, p. 18. 

 t Entomologist^ Txt-book, p. 236. 



