34 TIIK NTH-STORY OF INSECTS [CH. 



hours later the final moult takes place, a very delicate 

 cuticle bring shed and revealing the true imago. 

 Then follow the (lancing flight over the calm wateix 

 the mating and egg-laying, the rapid death. The 

 whole winged existence prepared for by the long 

 aquatic life may be over in a single evening; at most 

 it lasts but for a few days. 



In the development of the may-flies, then, we 

 notice not only a considerable divergence between 

 larva and imago, both in habitat and structure: we 

 see also what is to be observed often in more highly 

 organised insects a feeding stage prolonged through 

 the years of larval and nymphal life, while the winged 

 imago takes no food and devotes its energies through 

 its short existence to the task of reproduction. Such 

 division of the life-history into a long feeding, and 

 a short breeding period has, as will be seen later, an 

 important bearing on the question of insect trans- 

 formation generally, and the dragon-flies and may-flies 

 afford examples of two stages in its specialisation. 

 The sub-imaginal instar of the may-fly furnishes 

 also a noteworthy fact for comparison with other 

 insect histories. In two points, however, the life-story 

 of these flies with their aquatic larvae recalls that of 

 the cockroach. All the larval and nymphal instars 

 are active, and the wing-rudiments are outwardly 

 visible long before the final moult. 



