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, Libellula depressa. 

 (From Miall, aiter 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. 



