HEAD 



93 



term is very convenient in those cases where the structure cannot 

 be, or has not been, satisfactorily determined morphologically. 



In Figure 50 the parts usually visible on the anterior 

 aspect of the head and its appendages are shown so far as these 

 latter can be seen when the mouth is closed ; in the case of the 

 Insect here represented the bases of the mandibles are clearly 

 seen (r/), while their apical portions are 

 entirely covered by the labrum, just * 

 below the lower margin of which the 

 tips of the maxillae are seen, looking *- 

 as if they were the continuations of the 

 mandibles. 



The labrum is a somewhat perplex- 

 ing piece, morphologists being not yet 

 jiu'i'ced as to its nature; it is usually 

 placed quite on the front of the head, 

 and varies extremely in form ; it is 

 nearly always a single or unpaired 

 piece ; the French morphologist Cliatin 

 considers that it is really a paired 

 structure. 



The gula (Fig. 49, B d, and Fig. 47, 

 z) is a piece existing in the middle 

 L mgitudinally of the under-surface of the head ; in front it 

 bears the mentum or the submentum, and extends backwards 

 to the great occipital foramen, but in some Insects the gula 

 is in front very distant from the edge of the buccal cavity. 

 The epicranium forms the larger part of the head, and is con- 

 sequently most inconstant in size and shape ; it usually occupies 

 the larger part of the upper - surface, and is reflected to the 

 under-surface to meet the gula. Sometimes a transverse line 

 exists (Fig. 49, A) dividing the epicranium into two parts, the 

 posterior of which has been called the protocranium ; which, 

 however, is not a good term. The epicranium bears the antennae ; 

 these organs do not come out between the epicranium and the 

 clypeus, the foramen for their insertion being seated entirely in 

 the epicranium (see Fig. 50). In some Insects there are traces of 

 the epicranium being divided longitudinally along the middle 

 line. When this part is much modified the antennae may 

 appear to be inserted 011 the lateral portions of the head, or even 



L 50. Front view of head of 

 field -cricket (Gryllus] : , 

 epicranium ; b, compound 

 eye ; c, antenna ; d, post- : 

 e, ante-clypeus ; /, labrum ; 

 ff, base of mandible ; h, max- 

 illary palpus ; i, labial pal- 

 pus ; k, apex of maxilla. 



