iS 



ANTS. 



comprising an unpaired upper lip, or labrum, the mandibles, maxillae 

 and labium, or lower lip. In the last the originally separate and paired 

 embryonic appendages are fused in the median line so that they form 

 a continuous floor for the mouth or buccal cavity. In the cranium the 

 following regions may be distinguished: the front, a region bounded 

 anteriorly by the posterior edge of the clypeus and laterally by a pair 



of ridges, the frontal carinae or 

 laminae, just mesial to the inser- 

 tions of the antennae. A small, 

 usually triangular, median region, 

 the frontal area, can be easily 

 seen in the middle line just back 

 of the clypeus, and often there is 

 an impressed line, the frontal 

 groove, extending back from thi- 

 area over the middle of the front. 

 The frontal region passes with- 

 out definite boundary into the 

 vertex and temples, the former 

 extending posteriorly, the latter 

 lying above and behind the eyes. 

 The short region between the 

 vertex and the narrow opening, 

 or foramen through which the 

 alimentary tract and nervous 

 system pass into the thorax, may 

 be called the occiput. The 

 cheeks, or genae, comprise the 

 portions of the cranium anterior 

 to the eyes and lateral to the 

 frontal carinae. The ventral por- 

 tion of the head, bounded in 

 front by the labium, on the sides 

 by the cheeks and extending to 

 the occipital foramen, is the 

 throat, or gula. It is well-de- 

 veloped in the ants and is usually 

 divided into two equal halves by 

 a longitudinal suture. 



The mandibles, being the parts with which the ant comes into most 

 effective relations with its environment, present, like the beaks of birds 

 and the teeth of mammals, a bewildering variety of structure (Fig. 3). 



FIG. 4. External structure of head 

 in Myrmica nibra worker. (Janet.) A, 

 Dorsal aspect of head; B, anterior 

 aspect ; a. mandible ; b, clypeus ; c, 

 frontal area ; d, frontal groove ; e, 

 frontal carina ; /, vertex ; g, occiput ; 

 h, temple; /, base of antennal scape; 

 k, cheek: /, eye; ni, lateral ocellus; n, 

 median ocellus ; o, tentorial pit ; p, 

 labrum ; q, labium ; r, maxilla ; s, max- 

 illary palp : /, labial palp : it, gula. 



