MAYFLIES, DUNS AND SPINNERS 235 



be surprised to find them called the Pseudimago — a 

 name which has been condemned as etymologically 

 incorrect, being compounded of two words, one 

 Greek and the other Latin. Anglers call the sub- 

 imago of the smaller Ephemeridse a dun. The green 

 drake is the subimago of the genus Ephemera^' ■dsv<l 

 the march browai,the subimago of certain species of 

 the ^x^^ Ecdyurus. 



The subimago is not a perfect insect, its entire 



structure being enveloped in 

 Imago. a thin skin and covered with 



a multitude of tiny hairs or 

 cilice. Its movements are slow and its powers of 

 flight very limited. It takes shelter until it is ready 

 for the next change to the imago or perfect insect. 

 Once more it distends and splits its skin, and the 

 imago emerges, leaving behind a filmy envelope 

 retaining the form of the subimago, except that the 

 cast skins of the wings collapse. The imago is a 

 much more elegant and delicate creature than the 

 subimago ; its wings are transparent and glossy, its 

 body slender and tapering ; it is altogether better able 

 to fly than the comparatively heavy and ciliated insect 

 in the subimago stage. The legs of the imago are 

 longer than those of the subimago, as, too, are the 

 setae, and the forelegs and setse of the male are much 

 longer than those of the female. 



The lapse of time between the assumption of the sub- 

 imago or first winged form and the final metamorphosis 

 to the imago is largely dependent on temperature ; it 



