208 Aquatic Organisms 



The abdomen is long and slender. On the ventral side 

 of its second and third segments, far removed from the 

 openings of the sperm ducts, there is developed in the 

 male a remarkable copulatory apparatus, that has no 

 counterpart in any other insects. The venation of the 

 wings, also, is peculiar, nothing like it being found in 

 any other order. 



The dragonflies hold their wings horizontally in 

 repose. The damselflies are slender forms that hold 

 their wings vertically (or, in Lestes, obliquely outward) 

 in repose. Fore and hind wings are similar in form in 

 the damselflies; dissimilar, in the dragonflies. 



FIG. 115. A nymph of the damsel- 

 fly, Ischnura verticalis. 



The nymphs of the entire order are recognizable by 

 the possession of an enormous grasping labium, hinged 

 beneath the head. This is armed with raptorial hooks 

 and spines, and may be extended forward to a distance 

 several times the length of the head. It is thrust out 

 and withdrawn with a speed that the eye cannot follow. 

 It is a very formidable weapon for the capturing of 

 living prey. It is altogether unique among the many 

 modifications of insect mouth parts. 



Damselfly nymphs are distinguished by the posses- 

 sion of three flat lanceolate gill-plates that are carried 

 like tails at the end of the abdomen. The edges of 

 these plates are set vertically, and they are swung from 

 side to side with a sculling motion to aid the nymphs in 



swimming. 



