HEMIPTERA 353 



short on the middle line of the body but is much longer on each side 

 next to the compound eye; the epicranial suture is very indistinct in 

 the adult. In those bugs in which the paired ocelli are present they 

 are borne by the vertex. Immediately in front of the vertex is the 

 front or frons (Fig. 403, /). The clypeus is a narrow, elliptical sclerite 

 which is well defined (Fig. 403, c). Some writers on the Hemiptera 

 and Homoptera term the clypeus the tylus; but, for the sake of 

 uniformity, the use of this name should be discontinued. 



The four regions of the head referred to in the preceding paragraph, 

 the occiput, the vertex, the front, and the clypeus, are easily homol- 

 ogized with the corresponding regions in the more generalized insects. 

 We will now consider certain modifications of the structure of the 

 wall of the head that are correlated with the development of the type 

 of mouth-parts characteristic of the Hemiptera and Homoptera. 



On either side of the ch-peus there is what appears to be a pro- 

 longation of the front. In Lethocerus (Fig. 403, x, x), each of these 

 prolongations extends about half the length of the clypeus and 

 bounds the eye in front. It is believed that each of them represents 

 the basal part of a mandible ; they are termed, therefore, the mandibu- 

 lar sclerites. In some Homoptera the mandibular sclerites are dis- 

 tinct; this condition exists in the head of a cicada figured in the next 

 chapter (Fig. 463). The mandibular sclerites were so named by 

 Smith ('92), who first recognized that they pertain to the mandibles. 

 Before that time several different names were applied to them, which 

 are still in use by some writers; these are jugce, lorcB, and fulcra. 



In Lethocerus there is a pair of sclerites in front of the mandibular 

 sclerites and bounding the distal end of the clypeus; each of these is 

 the basal part of a maxilla; for this reason they are termed the 

 maxillary sclerites (Fig. 403, y, y) In Lethocerus the tips of these 

 sclerites meet on the dorsal wall of the head covering the tip of the 

 cl3"peus. 



On the ventral aspect of the head, the gula occupies the median 

 area (Fig. 404, gu); and the genes, the lateral areas (Fig. 404, ge). 

 In each gena there is a deep groove in which the ver\^ remarkable 

 antenna rests. 



At the front end of the ventral wall of the head there is a pair of 

 sclerites, each of which is articulated with a maxillary sclerite; these 

 are known as the bucculce and are believed to represent the maxillary 

 palpi (Fig. 404, bu). In Lethocerus the caudal margin of each buccula 

 is solidly joined to the front end of the gula. 



From the above account it can be seen that only a portion of 

 the mouth-parts enters into the constitution of the beak. The beak 

 consists of the following parts : the labrum, the labium, and four very 

 slender lancet-like organs enclosed in the labrum and labium, the 

 mandibular setae and the maxillary sets. 



The labrum is joined to the distal end of the clypeus ; in Lethocerus 

 the base of the labrum is covered by the maxillary sclerites, where 

 they overlap the tip of the clypeus, and its distal end extends into the 

 furrow of the labiiim, but the intermediate portion is exposed 



