CHAPTER XIII 

 ORDER ODONATA=' 



The Dragon-Flies and the Damsel-Flies 



The members of this order have four membranous wings, which are 

 finely netted with veins; the hind wings are as large as or larger than 

 the fore wings; and each wing has near the middle of the costal margin a 

 joint-like structure, the nodus. There are no wingless species. The 

 mouth-parts are formed for chewing. The metamorphosis is incomplete. 

 Dragon-flies and damsel-flies are very common insects in the 

 vicinity of streams, ponds, and lakes; they are well known to all who 

 frequent such places. The dragon-flies, especially, attract attention 



on account of their 

 largesize(Fig. 358) 

 and rapid flight, 

 back and forth, 

 over the water and 

 the shores ; the 

 damsel-flies (Fig, 

 359) are less likely 

 to be noticed, on 

 account of their less 

 vigorous flight. 



The name of 

 this order is evi- 

 dently from the 

 Greek word odous, 

 a tooth; but the 

 reason for applying 

 it to these insects is 

 obscure; it may refer to the tusk-like form of the abdomen. 



In these insects, the head is large; it differs in shape in the two 

 suborders as described below. The compound eyes are large; they 

 often occupy the greater part of the surface of the head ; in many 

 cases the upper facets of the eye are larger than the lower, and in a 

 few forms the line of division between the two kinds is sharply 

 marked. It is probable that the ommatidia with the larger facets 

 are night-eyes, and those with the smaller facets, day-eyes. See 

 pages 142 and 1 43 . Three ocelli are present. The antennae are short ; 

 they consist of from five to eight segments; of these the two basal 

 ones are thick, the others form a bristle-like organ. The mouth- 

 parts are well developed; the labrum is prominent; the mandibles 

 and maxillas are both strongly toothed; and the labiiun consists of 



Fig. 358. — A dragon-fly, Plathemis lydia. (From San- 

 born.) 



"Odonata: odous (65oi5s), a tooth. 



(314) 



