EXTERNAL ANATOMY OF INSECTS. U 



skull posteriorly .I' If description requires more definite limits, 

 parts may be intelligibly designated by their propinquity to 

 other parts. The shield is that part of the skull which is 

 immediately above the mouth, and whose office is to shield 

 it from injury. It was considered by Fabricius a part of 

 the mouth. It is described by him as a corneous porrected 

 part of the head, covering the mouth above, horizontally. It 

 is divided by him into two parts, the disk and the limb : the 

 limb is the upper lip, the disk is the true shield.'' It is 

 called by Straus-Uriickheim, &c., c/iaperon; by Kirby, nose. 

 In Lei)idoiHera, the shield is little apparent; it is hidden 

 by the scales. In Drptera, it is more readily distinguished. 

 In Hijmenoj)lera, it is very distinct ; you will recognize it, in 

 the large corneous piece embraced by the lower portion of the 

 eyes in the hornet.' In Coleoptera, it is sometimes obscure, 

 as in Hydrous;^ sometimes very conspicuous, as in Copris. 

 In Ortkoptera, it is always distinct. In several orders of this 

 class, the suture, uniting the shield with the upper part of the 

 skull, is membranaceous; hence the lip and shield move 

 simultaneously with the mandibles in mastication. This is 

 a departure from a general law of nature, and its occurrence 

 is well worth remarking ; as the motion of the shield might 

 induce an observer to suppose it the lip, which would conse- 

 quently become a new and supernumerary elementary part.' 

 In Hemiptcra, it is frequently raised and conspicuous, but its 

 limits are indistinct. In the central group, the dragon-flies, 

 it is raised, conspicuous, distinct, and horizontally divided into 

 two."' The Ejjicranium is the whole upper region of the 

 skull, bounded in front by the shield when distinct; laterally, 

 by the eyes ; and behind, by the junction of the head with the 

 prothorax. Its extent is greatest in Coleoptera ;^^ least, in 

 Diptera and Netiroptera." The Oculi, or eijes, are large 

 lateral portions of the skull, known to every one. The Ocelli, 

 or simple eyes, are small, highly convex lenses, soldered into 



< Necrophoriis . Head, with a distinct neck. — Stephens. 



^ Clypeus. Hori/.ontalis capitis pais cornea porrecta os superne tegens. a. discus 

 A. limbus. — Fabricitis. 



' Plate V. fig. le. 3!. k Plate V. fig. 1, and 3. if. 



' Je suis convaincuc lorsqu'on aura mieux examine la bouclie des insectes, 

 proprement dits, on troUTera quelle forme qu'cUe affecte elle est toujours esseii- 

 tiellement composee des mcmes Clemens. — Savigny. 



"> Plate V. fig. 15, X. ae. ■ Fig. 3. ^E. » Fig. 15. JE. 



