28 



GENERAL ZOOLOGY 



it 



The eggs, generally attached to water plants, hatch into 

 dark-colored, flattened aquatic nymphs. The mouth-parts 

 are unique in structure. The second maxillae are enlarged 

 and armed with hooks at the extremity. This formidable 



organ can be extended to seize 

 upon any insect within reach, and 

 when not so engaged it covers 

 the entire face like a mask, giv- 

 ing a peculiar and comical aspect 

 to a front view. The nymphs 

 breathe by means of tracheae, 

 which line the posterior portion 

 of the alimentary canal. When 

 water is drawn into the canal, 

 air is absorbed from it by this 



FIG. 15. Metamorphosis of Dragon-Fly. Natural size 



