The Stone-Flies 



upper lip. The full-grown nymph is not at all pupa-like and is 

 active. 



The enormous number of eggs laid by stone-flies indicates 

 that the chances of successful larval growth are rather small and 

 as a matter of fact these larvae are extensively eaten by fishes. It 

 makes no difference to the average fish whether he eats a carniv- 

 orous stone-fly larva or a vegetable-feeding May-fly larva. If 

 there were economic entomologists among the fishes these would 

 devote themselves to the destruction of the stone-fly larvae in 

 order that the general food supply of May-flies might be left un- 

 disturbed for fish food ! 



We have said that the larvae breathe by means of tracheal 

 gills. As a matter of fact, however, with some species there are 

 no such gills and no spiracles. These larvae must take their oxy- 

 gen from the water through the skin, the ultimate tracheae being 

 especially numerous in the spots where the spiracles would be if 

 there were any and the skin at this point is especially thin. This 

 method of breathing has been already mentioned in our accounts 

 of the larvae of the Chironomidae and of the larvae of the internal 

 feeding parasitic Hymenoptera. 



An aquarium student with an aquarium so constructed as to 

 maintain a constant current of water will do good service in 

 fully elaborating the life history of any of our common species. 



362 



