PSE UD ONE UR OP TERA . 



151 



beautifully marked with metallic green, or blue, while their larvae have external, leaf- 

 like gills. In ^sEschna and its allies the two pairs of wings are unequal, the abdomen 

 is cylindrical, and the species of large size, ^hile in the Lilelhdina the abdomen is 

 often flattened ; most of the dragon-flies belong to this latter group. 



220. 



219. 221. 



FIG. 219. Libellula quadrimaculata. FIG. 220. Nannophysa bella. FIG. 221. Agrion saucium, dragon-flies. 



The sexes often, as in Agrion and Libellula^ differ greatly in color, the males being 

 bright-colored, while the females are dusky and of one color. Moreover dimorphic 

 forms occur among dragon-flies, there being two sets of females, differing in the vena- 

 tion of the wings, one set resembling the males. 



SuB-OiiDER III. EPHEMERINA. 



The May-flies, forming the family EPHEMERID.E, differ so much from other Pseudo- 

 neuroptera that they may properly be referred to a distinct sub-order (Ephemerina). 

 These insects are called may-flies because many of them appear upon the wing in the 

 month of May, or early in summer. The name Ephemera is given in allusion to their 

 shortness of life, many of them living in the adult stage only a few hours, or no more 

 than a day, hence they are sometimes called 

 day-flies. They are among the most deli- 

 cate and fragile of insects, and their motions 

 during flight are exceedingly graceful. 

 West wood speaks of their elegant flight in 

 swarms (composed, as in the gnats, almost 

 entirely of male insects), in fine afternoons, 

 over or near water, alternately rising and 

 falling, and he states that in this opera- 

 tion the upward flight is produced by the 

 repeated action of the wings ; but that in 

 descending, the wings are widely extended, 



as well as the tails, or caudal filaments. FIG. 222. - Lachlania abnormis, enlarged. 



The head is small and rounded, the thorax 



is spherical, the pro thorax being small and collar-like, while the abdomen is long and 



slender, ending in two or three long, slender filaments. The wings are densely net- 



