ORDER ODONATA. 



The common dragon-flies of the suborder Anisoptera are 

 familiar to every one, but the damsel-flies, constituting the sub- 

 order Zyfjopiera, might not be recognized as also belonging to 

 this order. These damsel-flies are small narrow-winged forms, 

 which, like the butterflies, hold their wings back to back while 

 at rest. The Odonata have no quiescent pupal state; the 

 immature stages after the Q^g are collectively designated as 

 the nymph. The latter is always aquatic. It has highly 

 developed thoracic legs but no abdominal ones. Wing-pads 

 appear at the third or fourth molt. There are no external gill 

 structures except the three terminal appendages of the Zijgop- 

 tera. The abdomen of the nymph is slender among the 

 Ztjgoptera, but in the ordinary dragon-flies (Anisoptera) it is 

 rather short and broad. A very distinctive feature is the large 

 and elongate labium, folded beneath the body like an arm, the 

 "hand" of which, ending in a pair of claspers, covers the 

 mouth or the entire face. The nymphs crawl rather slowly, 

 often clumsily, but can dart some distance through the water 

 like the crawfish, being propelled by the sudden ejection of the 

 water in the rectal respiratory cavity. 



The Odonata and their near relatives the May-flies 

 [Epheinerida), isolated remnants of former insect life, in gen- 

 eral of primitive character although highly specialized along 

 some lines, are probably among the oldest orders of winged 

 insects. In younger groups the branching of the '' family tree" 

 of development may often be traced with some degree of satis- 

 faction by a study of the primitive characters retained by still 

 existing forms ; but in the lapse of ages so many of the earlier 

 lines of descent have been obliterated from the earth that in 

 the Odonata only the upper parts of a few separated branches 

 are traceable, their points of origin being involved in obscurity. 

 In Illinois the branch nearest the primitive stock is probably 

 that of the "black-wings," or Calopteryx, of our smaller streams, 

 representing the Caloptenjgkke. Another branch (Agrionidm), 

 including the more common damsel-flies, Agrion, Lestes, etc., 



