414 



tion of the epicranial suture, which is a Y-shaped line on the dorsum 

 of the head, near the caudal margin. Sutures are wanting, separating 

 vertex from occiput, occiput from postgenae, and postgenae from 

 genae. The vertex occupies that part of the dorsum of the head cap- 

 sule caudad of the arms of the Y; and the occiput and postgenae 

 together, the portion of the caudal aspect of the head not occupied by 

 the occipital foramen and the compound eyes. The genae are the areas 

 mesad of the ventral margins of the compound eyes. They fuse with 

 the postgenae (Fig. 7, pg) near the ventral margin of the head. 

 Extending caudo-dorsad on the caudal aspect from the ventral articu- 

 lations of each mandible, there is a distinct ridge which disappears 

 near the middle of the head. The trochantins of the mandibles are 

 present as indistinct triangular areas laterad of the bases of the mandi- 

 bles (Fig. 7, tm). 



Compound Byes. — The compound eyes of the nymphs, like those 

 of the adult, are very large. They occupy perhaps one-third of the 

 dorsal surface of the head, nearly the whole of the lateral surface, 

 and part of the ventral. The facets are hexagonal and similar to those 

 of other insects. 



Ocelli. — The ocelli are wanting during nymphal life, but in the 

 later stages the adult ocelli may be seen through the transparent cuticle 

 of the dorsum of the head. Thus it often appears as if the nymph 

 had ocelli when in reality there are none present, as can be proved by 

 an examination of the final exuvium, or by dissection. 



Antennae. — The antennae, in all full-grown nymphs, consist of 

 seven segments. The distal segment is short in most species and the 

 connection between it and the preceding one is frequently obscure, so 

 that it seems as if the appendage had only six segments. The first 

 segment is usually thicker than the remaining ones, and in the 

 Agrionidae is as long as all the rest of the segments together. In the 

 Coenagrionidae, the third segment is the longest and each of the seg- 

 ments distad of it is shorter than the segment preceding. The two 

 proximal ones are not constant in length but are always shorter than 

 the third. 



Mandibles. — The mandibles are normally hidden from sight by 

 the large labium and the flap-like labrum. They are located on the 

 ventral surface of the head and are well formed for mastication. They 

 are irregular in outline, though somewhat rectangular, bearing four 

 short, strong teeth along the distal margin and several smaller teeth 

 mesad and proximad of these. 



Maxillae. — The maxillae (Fig. 22) are attached to the ventral 

 surface of the head and the following parts are distinguishable : a 



