2l6 FIELD ZOOLOGY. 



of the May flies, a moulting occurs after acquiring wings; 

 this is called a subimago stage, and is a phenomenon not 

 known to occur elsewhere. This stage may last from a 

 few minutes to twenty-four hours. Such unusual exten- 

 sions of the adult stage as are known to occur, seem to 

 have relation to this subimago stage, the adult life of the 

 different species after this subadult moult is undergone, 

 being nearly uniform in length. 



