METAZOA INSECTA. 401 



and first pair of maxillae. It can be thrown out as rep- 

 resented in the figure, and the teeth at the end serve to 

 catch the prey. 



According to Packard, 1 it was owing to the fact that 

 the second pair of maxillae were armed with teeth that 

 the name Odonata (from the Greek meaning tooth) was 

 given to this order. Calvert 2 remarks, however, that th'e 

 name refers " presumably to the toothed mandibles." 



The adult has small eyes, comparatively speaking; the 

 labium is reduced in size and the parts are more concen- 

 trated than in the larva, although much more loosely con- 

 nected than in the specialized dragon-flies. 



In many ways Agrion (No. 966) resembles Calopteryx. 

 Its young is provided with three caudal gills. The head 

 of the adult is broad with the eyes on the sides, and the 

 labium is short. The wing venation is simple and the 

 flight is not swift. The long slender abdomen is used as 

 a rudder and is sometimes brilliantly colored in both 

 genera. 



The most specialized Odonata are represented by 

 Aeschna and Plathemis (== Libellula). Aeschna (PI. 967 ; 

 No. 968) is one of our largest dragon-flies. The eyes 

 are separated in the larval and pupal (PI. 967, A. grandis 

 Linn.) stages but meet on top of the head in the adult 

 (No. 968, A. heros Fabr.). The wing muscles are strong 

 and the flight is swift, the insect darting like an arrow. 



Plathemis is another swift flier. Its eggs, like those of 

 most Odonata (see No. 969), are laid on aquatic plants or 

 dropped in the water. The young (No. 970 ; PI. 97 j, fig. 

 i) possesses the long unconsolidated body and the simi- 

 lar thoracic segments of the adult Thysanura and the 

 larval Ephemeridae, but in many respects it has become 

 specialized. The labium is modified into a mask (No. 

 972) that completely covers the other mouth parts. The 



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1 Ent. for Beginners, 1889, p. 346. 



2 Trans. Amer. Ent. Soc.. Phila., XX, 1893, p. 153. 



