46 INSECTS. 



have essentially the same structure, a double fold of 

 membrane supported by chitiiious veins, and they are 

 very similar in development. 



Study of the Nymph. Place a large nymph in a small 

 dish with just enough water to cover it, and study it 

 alive, with the aid of a good lens. Observe : 



1. Its sturdy form. 



2. Its large eyes. 



3. Its short antennce. 



4. Its enormous lower lip, covering the lower and front 

 parts of the head. Seize the edge of it with fine -pointed 



forceps, and pull it forward for exami- 

 nation. Note that it is so jointed to 

 the head that it can be extended far 

 forward, and quickly retracted. Note 

 that it is two-lobed, that the lobes are 

 triangular, that each bears an incurved 

 hook at the apex, that each is toothed 

 along its inner margin, and that the 

 A DRAGON-FLY NYMPH, whole is a very formidable grasping 

 organ. 



5. Its mouth, with well-developed mandibles and max- 

 illse inside the labium. 



6. Its rudimentary wings. Compare with those of the 

 adult. 



7. Its well-developed legs. Compare them in position 

 with the legs of the adult. 



8. The regular expansion and contraction of its abdo- 

 men in respiration. Note the striking unlikeness of the 

 respiratory methods in the adult and in the nymph. 

 The adult lives exclusively in the air ; the nymph, exclu- 

 sively in the water. Both must get oxygen from the 

 air. Internal branching and intercommunicating air tubes, 

 which open exteriorly at the spiracles in the adult, con- 



