THE GILL-CHAMBER OF DRAGONFLY NYMPHS 343 



where it emerges among the appendages of the abdomen. The 

 three lobes are hinged at their base, and the one on the dorsal 

 border of the anus laps over the two lateroventral lobes when 

 closed. My own observation corroborates this, and figure 44 

 shows the appearance from the dorsal side with one appendage 

 removed. The edge of each valve-flap bears a row of fine hairs; 

 the three valves fit together perfectly and seem to make a water- 

 tight joint. Outside of each lobe there is, in my material, a simi- 

 lar set of fleshy folds, which seem to provide bases on which the 

 lobes rock. The action of the valve is often conspicuous : it opens 

 and shuts with every suction of water in some nymphs. 



The anal valve is present in all the nymphs which I have 

 studied. In the Aeschnidae the lobes are less heavily chitinized; 

 in Basiaeschne, as figure 45 indicates, they are rather membran- 

 ous and wrinkle when holding the rectum closed. In Gomphus 

 they are more chitinous. 



THE ZYGOPTERAN RECTUM 



Dufour ('52) states that Galop teryx virgo nymphs have three 

 richly tracheated cushions, free at the caudal end, and hanging 

 into the lumen of the rectum. This is denied by some, affirmed 

 by others. Dewitz ('90) claimed that rectal gills are present in 

 the Agrionidae. 



My own work covers five species of this suborder, chosen 

 from a wide range within it. The recta of four of the forms, 

 Lestes forcipata, Argia putrida, Enallagma hageni, and Gora 

 chirripa, as well as Mecistogaster modestus, studied by Galvert 

 ('11), may be dismissed with the statement that they have 

 only the usual longitudinal rectal glands, similar to those in 

 other orders of insects. The number of these is three or six. 

 There is no tracheation beyond a single small branch from each 

 dorsal trunk; nothing approaching a breathing mechanism. 

 These recta are not in any way enlarged. 



The rectum of Galopteryx maculata is expanded into a globe 

 and has three large pads, one middorsal and the other two 

 lateroventral. From the sections made by Dr. Galvert, which 

 he was kind enough to let me use, it is evident that these are 



