70 EPHEMEROPTERA. 



stitute Ephemeroptera {i<f>T^fX€pov, short-lived insect, 

 TTTcpov, a wing) for Plectoptera as the name of the 

 order, and this avoids the confusion that arises from 

 the use of the words " Plectoptera " and " Plecoptera," 

 which are not only similar in their orthography, but 

 the same in signification. The abdomen has two or 

 three long, thread-like setae or stylets (se). Some 

 May-flies in their adult stage live only a few hours 

 (hence the name of "day-fly"), though others live 

 several days. The larval and pupal existence covers, 

 however, as is often the case, a much longer time, 

 lasting for a period of two or three years, and is 

 passed wholly in the water. PL III., Fig. 30, is the 

 larva ; its respiratory organs are in the form of gflls 

 and are attached to the sides of the abdomen. 



The larvae and pupae shed their skin many times. 

 One genus, Chloeon, according to Lubbock,^ moulted 

 twenty-one times before reaching its full growth. The 

 winged insect that first appears from the pupa skin 

 is not the true imago, but represents a transitional 

 stage, which has been called the subimago, and it is 

 not till this subimago has cast its skin that the mature 

 May-fly is seen. This is one of the few instances 

 in which insects with fully developed wings continue 

 moulting. 



One species of this family, the Oligoncui'ia rhenana, 

 is white. According to Kirby, it appears in such vast 

 numbers on the Rhine after sunset as to resemble fall- 

 ing snow-flakes. In the morning nearly all, if not all, 

 are dead. Morse has shown how myriads of Ephem- 



1 Trans. Linn. 6'^r., London, 1863, 1865. 



