310 



AN INTRODUCTION TO ENTOMOLOGY 



veins, with which primarily it was connected only by cross-veins. 

 The veins labeled IMi, IM3, and ICui in Figures 353 and 354 are 

 good illustrations of this type of veins. The initial I in these designa- 

 tions is an abbreviation of the word intercalary. Thus the intercalary 

 vein between veins Cui and Cu2, i. e., in the area Cui, is designated 

 as vein ICui. 



Figures 353 and 354 will aid in the determination of the homol- 

 ogies of the wing-veins of May-flies. In these figures convex veins 



are designated by 

 plus signs and con- 

 cave veins by minus 

 signs. In attempt- 

 ing to determine 

 the homology of a 

 vein in a wing 

 where the venation 

 is reduced, it should 

 first be determined 

 whether the vein is 

 convex or concave, 

 as the corrugations 

 of the wings of 

 May-flies are the 

 most persistent fea- 

 tures of them. For 

 a more detailed ac- 

 count of this subject, see Chapter X of "The Wings of Insects." 



The Greek name Ephemeron applied to these insects in the days 

 of Aristotle was derived from ephemeras, signifying lasting but a day; 

 and from that time to this, frequent references have been made to the 

 insects that live only a single day. This brevity of the life of these 

 insects is true only of their existence in the adult state. Strictly speak- 

 ing, the May-flies are long-lived insects; some species pass through 

 their life-cycle in a few weeks in midsummer ; but as a rule one, two, or 

 even three years are required for the development of a generation. 

 The greater part of this time is passed, however, beneath the surface 

 of water, and after the insect emerges into the air and assumes the 

 adult form its existence is very brief. With many species the indi- 

 viduals leave the water, molt twice, mate, lay their eggs, and die in 

 the course of an evening or early morning; and although the adults 

 of many genera live several days, the existence of these insects is 

 very short compared with that of the adults of other insects. 



The females lay their eggs in water. Some short-Hved species 

 discharge the contents of each ovary in a mass. Individuals are often 

 found in which there project from the caudal end of the body two 

 parallel subcylindrical masses of eggs, one protruding from each of 

 the openings of the oviducts. "The less perishable species extrude their 

 eggs gradually, part at a time, and deposit them in one or the other 

 of the following manners: either the mother alights upon the water 



354. — Hind wing of Chirolonetes alhomanicatiis. 



