CHAP. XXI INSECTA : NEUROPTERA 309 



throw off still another skin, after which their development 

 is complete, and the mature insects (known to anglers as 

 " Grey Drakes ") enter upon the last, short but merry, phase 

 of their existence. 



All through their previous life feeding has been their 

 chief activity; now they feed no more. For a brief half -hour, 

 or at most duiing the few short hours of a summer night, the 

 fragile little flies dance in swarms together up and down, 

 sometimes high in the air, often so close to the water that 

 the whisks at the end of their tails sweep the surface. Now 

 they are about to fulfil the function which distinguishes this 

 phase of their life — now they mate, and each female drops ori 

 the surface of the water a batch of small disc-shaped eggs, 

 which slowly sink, scattering as they do so. Their destiny 

 is now fulfilled, and gradually the myriad flies that filled the 

 air sink and die. 



For several nights in succession such hosts of May-flies 

 will rise from the same piece of water, and the same pheno- 

 menon can be witnessed ; then all is stiU, and the future of 

 the race is hidden in the life-germs within the eggs that lie 

 deep in the water. 



^ ^ The larvae of most of the different genera of 



May-fly live in running water, but Ephemera 

 vulgata is very common in ponds and ditches, as well as in 

 slow-running streams. As soon as the larva escapes from 

 the egg, it burrows in the mud at the bottom of the water, 

 thus gaining protection from its enemies. It has at first no 

 trace of wings, but merely a little, segmented, rather worm- 

 like body, with, however, a pair of long antennae and six 

 legs. Slowly, accompanied by many moults, the development 

 proceeds, until a full-grown larva or nymph exhibits the 

 form shown in Fig. 230. Attached to the thorax can be 

 seen the rudiments of two pairs of wings, and projecting 

 freely from the abdomen on each side is a series of narrow 

 plate-like gills, fringed with respiratory hairs.^ The tracheae 

 send closed branches into these gills, for they are typical 

 " tracheal gills " ; by waving them about in the water, 

 diffusion of fresh air into the tracheae is facilitated. 



At the end of the tail are three longer processes which are 

 additional respiratory organs of a peculiar and unusual kind, 

 ^ The form and position of the gills vary in different genera. 



