THE SIALID.E : THE ALDER 



81 



several months, during which phase it gradually 

 matures and attains by progressive changes a state 

 ready for metamorphosis. When this is reached it 

 swims to the surface, crawls ashore, attaches itself to 

 stone, rock, or timber, and undergoes a direct meta- 

 morphism into its imago existence. 



Its appearance at first is delicate and pale, and it 

 appears to have a great difficulty in flying; but its 

 colour soon darkens, and it grows stronger on the 

 wing. 



In Plate XIV., Fig. 3 shows the larval stage of the 

 Perlidse Nemura variegata (Old Joan), magnified 

 about two and a half diameters. The characteristic 

 wings of this water insect are to be seen on either 

 side of its body, and the larva is shown just before it 

 undergoes its metamorphosis. 



The following are some well-known forms of the 

 Perlidse : Stone-fly, Yellow Sally, etc. 



THE SIALID^E : THE ALDER 



The sub-aqueous existence of this form of insect life 

 is purely larval. 



The eggs are laid by the female Alder on grass, 

 rushes, etc. When the young larva is hatched, it 

 crawls into the water and continues its existence 

 more or less in the shelter of the mud until it is ready 

 for its pupal stage. 



It then leaves the water again, and burrows in the 

 earth to pass its^pupal existence ; it there assumes the 



6 



