438 



the caudal valves are always serrate. 



Variations in the ovipositor of the female are seemingly of little 

 importance in classification although there is enough difference in the 

 apical sternites (sti.s) of the eighth segment alone to facilitate the sep- 

 aration of genera. 



Life History and H.a.bits 



The metamorphosis of all Odonata is incomplete and the life his- 

 tory relates to the egg, nymph, and adult. 



EGG 



The eggs of Zygoptera are elongate and ovoidal, their length being 

 much greater than their transverse diameter. In length they average 

 about one millimeter; in diameter usually about one-fourth of this. 

 They are inserted cither above or below the surface of the water in 

 the stems of plants. Lestes and related genera insert the eggs con- 

 siderably above the level of the water, and several instances are re- 

 corded in which the plants suffer from excessive oviposition. Most 

 of the Coenagrioninae oviposit beneath the water upon the submerged 

 parts of plants. To accomplish this, the female with the male clinging 

 to her alights on a projecting part of a plant and backs down into the 

 water dragging tlie male with her. She often goes so far beneath the 

 surface that I)oth are completely suljmcrged. Kellicott ('99:24) 

 observed the females of Argia moesta puirida descend into the water 

 in this fashion; and I have frequently .seen EiMllagiiia sigiiatiDii de- 

 scend into the water to oviposit and, less frequently, Jschmtra z'crticalis 

 and Enallagiiia aiitciinatuni. It is probable that many more of the 

 subfamily Coenagrioninae enter the water to find a suitable place for 

 oviposition. The egg-laying habits of the Agrionidae have not been 

 extensively studied; but Kennedy ('15:339) reports that Agrioii 

 acquabilc variety yakuna deposits the eggs beneath the surface of the 

 w-ater upon willow roots, and is unaccompanied by the male. Need- 

 ham also says that Agrion tiuiciilatum oviposits just beneath the sur- 

 face of the water, but Wesenberg-Lund ('13) ol)ser\cd a luirojiean 

 species depositing eggs above the water. In all cases tlic female was 

 unaccompanied by the male. 



The number of eggs laid by a single female has been but partially 

 investigated, owing to the great tlillicultv of intlucing the female to lay 

 in captivity. A number of adults were dissected with a view to discov- 

 ering the egg-laying capacities of the group. Several reared specimens 

 whicii had no chance to deposit eggs were found to contain as many 



