ODONATA 59 



spines. Its palpi are modified into a pair of grasping 

 lateral lobes. These are flat and naked in the nymphs 

 of the darners but in the skimmers they are broad and 

 concave, and when closed together the tip of the labium 

 is spoonshaped and covers the face almost up to the 

 eyes. No other creature has a lip like this. It is quite 

 distinctive of this order of insects. 



II. In the thorax. 



1. The relatively greater size of the pro thorax. 



2. The backward extension of the hind legs. 



3. The inverted position of the wing cases, the hind wing 

 on top, as in grasshoppers. 



III. In the abdomen. 



1. The ten free segments. 



2. The wide expansion at the rear, providing space for 

 the gill chamber in which the alimentary canal ter- 

 minates. 



3. The five sharp spines at its tip: between these are three 

 minute valves that guard the opening into the respira- 

 tory chamber. Through their fringed edges the water 

 is strained as it enters. 



In the damselfly nymph, the most noteworthy differences 

 are in the slenderness of the body and in the respiratory 

 apparatus. There is no internal gill chamber, but instead 

 there are three large, oval, platelike gills attached to the 

 tip of the abdomen. The air tubes entering these have 

 already been noted (p. 25). 



