MAY-FLIES 



431 



The legs throughout the family exhibit a considerable variety of 

 structure, and the front pair in the males of some species are remark- 

 ably long. The abdomen is usually slender, and consists of ten 

 segments ; the terminal one bears three, or two, very long flexible 

 appendages. The first dorsal plate of the abdomen is either 

 wanting or is concealed to a considerable extent by the meta- 

 notum. The wings 

 are peculiar ; the an- 

 terior pair vary a 

 great deal in their 

 width, but are never 

 very long in propor- 

 tion to the width ; 

 the hind pair are 

 always dispropor- 

 tionately small, and 

 sometimes are quite 

 wanting. The vena- 



FIG. 275. Wings of Ephemera danica. (After Eaton.) 



tion consists of a few, or of a moderate number, of delicate longi- 

 tudinal veins that do not pursue a tortuous course, but frequently 

 are gracefully curved, and form a system of approximately similar 

 curves, most of the veins being of considerable length ; close to the 

 anterior margin of the wing there are two or three sub-parallel 

 veins. Frequently there are very numerous fine, short cross- 

 veinlets, but these vary greatly and may be entirely wanting. 



The earlier stages of the life of Ephemeridae are, it is believed, 

 in the case of all the species, aquatic. May-flies, indeed, during 

 the period of their post-embryonic development are more modified 

 for an aquatic life than any other Insects, and are provided with 

 a complex apparatus of tracheal gills. The eggs are committed 

 to the waters without any care or foresight on the part of the 

 parent flies, thus the embryonic development is also aquatic; 

 little, however, is known of it. According to Joly l the process 

 in Palingenia virgo is slow. The larva on emerging from the 

 egg has no respiratory system, neither could Joly detect any 

 circulation or any nervous system. The creature on emergence 

 is very like Campodea in form, possessing long antennae and tails 

 caudal setae. Owing to the organisation being inferior, the 

 creature in its earlier stages is called a larvule ; in its later stages 

 1 Mem. Ac. Sci. Toulouse (7), iii. 1871, p. 379. 



