163 



on rapid places." What Cotton says about 

 the season of this fly, may be taken as a 

 general rule, "The green-drake comes in about 

 the 20th of May, or betwixt that and the 

 latter end, (for they are sometimes sooner, 

 and sometimes later, according to the quality 

 of the year), but never well taken till towards 

 the end of this month, and the beginning 

 of June." Mr. Hansard observes, " The 

 green-drake is in season from the 20th of May 

 till the 20th of June, but it is most plentiful just 

 at the end of the one month and the beginning 

 of the next; a dry season and low water is 



impregnated with some nutritious substance which the 

 insect's organisation appropriates. After having sojourned 

 within these dens for nearly two years, and changed them 

 as often as its increase of bulk demanded a more spacious 

 lodgment, the insect undergoes those transformations 

 which permit it to enjoy in another element a momentary 

 existence. Nevertheless, short as this term of life is, the 

 insects are surrounded at the very threshold of their new 

 existence with the most imminent peril. The transforma- 

 tion which is to convert the aquatic into the aerial being, is 

 attended with all those risks which we have seen attend the 

 gnat: the ephemera is at the mercy of a gust of air; if 

 once thrown off its balance while endeavouring to extricate 

 itself from its larval skin, it is lost for ever ; for it has no- 

 thing to dread so much as the element in which it has lived 

 so long. When, however, the insects have once become 

 fitted for their new mode of life, they burst at sunset from 

 the banks of the river which they have inhabited in incre- 

 dible numbers. It is thus that these creatures burst forth 

 from the waters : it would appear, however, that though 

 the time of the year in which they become aerial beings 

 differs in different countries, yet the insects of the same 



