92 HEAD CHAP. 



(j^uite separate pieces, though we are in the habit of speaking of 

 them as if such were the case. If an Insect be distended by 

 pressure from the interior, many of tlie sclerites can be forced 

 apart, and it is then seen that they are connected by delicate 

 membrane. The structure is thus made up of hard parts meeting 

 one another along certain lines of union — sutures — so that the 

 original membranous continuity may be quite concealed. In 

 many Insects, or in parts of them, the sclerites do not come into 

 apposition by sutures, and are thus, as it were, islands of hard 

 matter surrounded by membrane. A brief consideration of some 

 of the more important sclerites is all that is necessary for our 

 present purpose : we will begin with the head. 



The head is most variable in size and form ; as a part of its 

 surface is occupied by the eyes and as these organs differ in 

 shape, extent, and position to a surprising degree, it is not a 

 matter for astonishment that it is almost impossible to agree as 

 to terms for the areas of the head. Of the sclerites of the head 

 itself there are only three that are sufficiently constant and 

 definite to l)e worthy of description here. These are the clypeus, 

 the epicranium, and the gula. The clypeus is situate on the 

 upper surface of the head-capsule, in front ; it bears the labrum 

 which may he briefly described as a sort of flap forming an upper 

 lip. The labrum is usually possessed of some amount of mobility. 

 The clypeus itself is excessively variable in size and form, and 

 sometimes cannot be delimited owing to the obliteration of the 

 suture of connexion with the more posterior part of the head ; 

 it is rarely or never a paired piece. Occasionally there is a 

 a h tf a more or less distinct piece 



(^""j^^^^Lj, '^©.^fcT^Ty'^ interposed between the 



a •" (-V)"'^ e..'-^^^^^^\ clypeus and the labrum, 

 1 h \ % i ^^^^ which is the source 



""[ 1 L^ {~.\ -Ij of considerable difficulty, as 



i,-.-!^^^^^^^ ' 'W ,. X""'„.g^^fi.d ^^ ^^^y ^■'^ taken for the 

 '-^ ^^~- — ^^-^"^ clypeus. Some authors call 



Fig. 49.-Cap.s„le of head of beetle, ffarpalus *^^^ '^^^P^"^ ^^^^ epistomC, but 



caliginosiis : A, upper ; B, under surface : a, it is better to USe this latter 



clypeus ; b, epicranium ; c, protocranium ; 4-„^,„ i?„„ ii e ■ t 



,t, gula; e, facette.l eye;/, occipital fora- ^^^^^^ ^°^ ^^^^ purpose of mdl- 



men ; g, submentum ; h, cavity for insertion catiug the part that is imme- 



of antenna. t i i i i . 



diately behind the labrum, 

 whether that part be the clypeus, or some other sclerite ; the 



