PHYLUM ARTHROPODA 339 



dition of the egg ducts of the female is also unique. Adult may- 

 flies probably take no food; they mate, lay their eggs, and, after 

 a few hours, die. 



Order 3. Odonata. DRAGON-FLIES AND DAMSEL-FLIES 

 (Fig. 262). Insects possessing four membranous wings, with 

 many cross veins; hind wings as large as or larger than fore- 

 wings; each wing with joint, the* nodus, on front margin; biting 

 mouth-parts; metamorphosis incomplete. 



The dragon-flies are also called darning-needles and snake 

 doctors. When at rest they hold their wings horizontally, differ- 

 ing in this respect from the damsel- flies, which hold their wings 



FIG. 262. Order ODONATA. A dragon-fly, Libettida depressa. 

 (From Miall, alter Charpentier.) 



vertically over their backs. The adult dragon- flies devour large 

 numbers of mosquitoes, but unfortunately feed only by day, 

 whereas some of the mosquitoes are most active after dark. 

 The young live in the water; they breathe by drawing in and 

 expelling water from the rectum, which is lined with tracheal 

 gills. The damsel- flies are more delicate than the dragon- flies. 

 Their young possess leaf-like tracheal gills at the posterior end 

 of the body. The compound eyes of the ODONATA are made 

 up of an enormous number of elements (ommatidia) ; more than 

 30,000 facets have been counted in the eye of one species. 



