38 



^A^ INTRODUCTION TO ENTOMOLOGY 



Fig. 46. — Head of 

 a cockroach ; m , 

 muscle impres- 

 sions. 



In the more generalized insects at least, if not in all, the front 



bears the median ocellus; and in the Plecoptera, the paired ocelli also. 



Frequently the suture between the front and the following sclerite, the 



clypeus, is obsolete ; but as it ends on each side in the invagination 



which forms an anterior arm of the tentorium or 



endo-skeleton (Fig. 46, at), its former position can 



be inferred, at least in the more generalized 



insects, even when no other trace of it remains. 



In Figure 46 this is indicated by a dotted line. 



The clypeus. — The clypeus is the intermediate 

 of the three unpaired sclerites between the epi- 

 cranial suture and the mouth (fig. 46, c). To this 

 part one condyle of the mandible articulates. 



Although the clypeus almost always appears 

 to be a single sclerite, except when divided trans- 

 versely as indicated below, it really consists of a 

 transverse row of three sclerites, one on the median line, and one on 

 each side articulating with the mandible. The median sclerite may 

 be designated the clypeus proper, and each lateral sclerite, the ante- 

 coxal piece of the mandible. Usually there are no indications of the 

 sutures separating the clypeus proper from the antecoxal pieces ; but 

 in some insects they are distinct. In the larva of Corydalus, the ante- 

 coxal pieces are not only distinct but are quite l^-rge (Fig. 47, ac, ac). 

 In some insects the clypeus is completely or partly divided by a 

 transverse suture into two parts (Fig. 45). These may be designated 

 as the first clypeus and the second clypeus, respectively; the first 

 clypeus being the part next the front (Fig. 

 45, Cy) and the second clypeus being that next 

 the labrum (Fig. 45, Co). 



The suture between the clypeus and the 

 epicranium is termed the clypeal sutiire. 



The labrum. — The labrum is the movable 

 flap which constitutes the upper lip of the 

 mouth (Fig. 45, L). The labrimi is the last of 

 the series of unpaired sclerites between the 

 epicranial suture and the mouth. It has the 

 appearance of an appendage but is really a 

 portion of one of the head segments. 



The epicranium.^ — Under the term epi- 

 cranium are included all of the paired sclerites of the skull, and some- 

 times also the front. The paired sclerites constitute the sides of 



ig. 47. — Head of a 

 larva of Corydalus, 

 dorsal aspect. 



