422 



Abdomen. — The abdomen is always composed of ten complete 

 body-rings. The eleventh segment, seen best in Lestes, is represented 

 by the small basal processes (Figs. 5, 18; An) to which the caudal 

 gills are attached. The twelfth segment, supposed to be present in 

 the minute sclerites bounding the anus, is apparently wanting or indis- 

 tinct. Each body-ring is without sutures but is roughly divided by 

 the lateral carinae into sternal and tergal areas. In the Coenagrionidae, 

 the lateral carinae of the first eight segments are known as lateral 

 keels (Fig. 25, Ik). In Lestes, the caudal extremity of each keel is 

 sometimes drawn out into short setae and is setose or hairy along the 

 margins. Marginal setae are also present in the Coenagrionidae but 

 the heavy caudal setae are wanting. 



Sexual Appendages. — It is claimed that the sexual appendages of 

 the nymphs (Balfour-Brow^ne, '09) can not be seen and differentiated 

 until about the time of the seventh molt. From personal observations, 

 however, it would seem that the appendages appear much earlier than 

 this, and possibly as early as the fourth molt. The male genital ap- 

 pendages are located on the ninth abdominal sternum and consist of 

 a simple pair of short, sharp, conical styli, near the ventro-meson. 

 There is also an indication of the location of the male copulatory 

 organs on the ventral surface of the second and third sterna (Fig. 

 24, ag), though nothing definite is formed there until the adult 

 emerges. The ovipositor of the female is composed of six processes 

 developing from the eighth and ninth sterna (Figs. 5, 18; oce, oca). 

 Four of these are similar in appearance, being slender, curved, blunt 

 projections extending commonly beyond the end of the ninth segment 

 and frecjuently beyond the apex of the tenth. Laterad of this double 

 pair of inner valves, can be found a pair of lateral styli which differ 

 from the inner valves in being pointed at the tip and much broader at 

 the base. The origin of the four median valves is partly from the 

 eighth abdominal segment and partly from the ninth, the external 

 ventral pair (oce) being derived from the eighth. 



Caudal Gills. — The caudal tracheal gills are present in the earliest 

 stages and are reported to have been seen in the embryo. They vary 

 from linear to broadly obovate in outline and from triangular to 

 linear in cross-section. Cuticular pigmentation, if any, is either in 

 transverse bands or is diffused over the entire gill. In many cases 

 the tracheae contain pigment, which causes them to stand out in 

 marked contrast to the rest of the gill. Along the margin of the gills 

 are rows of spines or setae, which differ in number and extent in dif- 

 ferent species. The lateral median ridges of the flat type of gills also 

 possess rows of setae, but they are difficult to observe and are of little 



