425 



Ocelli. — The location of the ocelli has already been described. They 

 are moderately large, elliptical, and grouped in a triangle (Fig. 32, o). 



Compound Byes. — The compound eyes (Figs. 30, 32; ce) are 

 large and contain a large number of ommatidia. They are located 

 mostly on the lateral aspects of the head, but sometimes extend well 

 onto the dorsum. 



Antennae. — The antennae (Fig. 32, ant) are usually composed of 

 four segments. The condyle of the scape is especially prominent. 

 The two terminal segments are styliform and resemble a single seg- 

 ment. The greatest variation in the different segments lies in the 

 length of the first, which ranges from hardly more than half that of 

 the second segment, to an equal or greater length than that. There 

 is also a less noticeable variation in the length of the third segment. 



Labium. — The labium (Fig. 37) is the ventral movable appendage 

 of the head. It is a broad flat piece and covers nearly one-fourth the 

 entire ventral surface. The submentum (sm), the proximal sclerite, is 

 attached to the head and neck and comprises that part of the labium 

 dorsad of the hinge when the labium is at rest. Immediately cephalad 

 of the hinge there is a small, almost linear, transverse area, the mentum 

 (me). Beyond this there is a large subtriangular piece with a deep me- 

 dian, distal cleft and a suture-like furrow extending to the proximal 

 end. This piece is the median lobe (ml) and represents fused glossae 

 and paraglossae. On each side of this median lobe there are heavy 

 blade-like lobes, the labial palpi, which connect with the proximal part 

 of the median lobe. The fixed proximal segment is the palpiger (pi), 

 the large movable distal portion is the pro.ximal segment of the palpus, 

 and the short blunt movable appendage borne by the proximal segment 

 is the distal segment (Ipi, Ip^). There is a long, sharp, fixed hook 

 mesad of the distal segment of the palpus, which in most cases is 

 longer than the distal segment of the palpus. 



Maxillae. — The maxillae are just above the labium, one on each 

 side of the mouth-opening. When the labium is applied to the ventral 

 surface of the head, the maxillae are hidden, except the cardines and 

 the caudal half of the stipites. The cardo and cardella are bent at 

 an angle^to the stipes, but when removed from the head along with the 

 rest of the maxilla they are seen as two small sclerites attached to the 

 proximal end of the stipes, the cardo being triangular and attached to 

 the stipes, and the mesal side of the triangle forming the suture be- 

 tween cardo and cardella. The cardella (Fig. 28, cl) is a very irreg- 

 ular sclerite which articulates with the head capsule. Attached to the 

 distal border of the stipes, the quadrangular sclerite which forms the 

 body of the maxilla, are two appendages, the lateral more slender two- 



