A LITTLE ENTOMOLOGY 59 



are apparently able to emerge without effort and 

 almost instantaneously. 



The newly fledged insect is known as a dun or sub- 

 imago. It is not yet fit for long flights, but is keen 

 to test its wings. Those which do not require a 

 grip of dry land before they can enter upon their 

 aerial life, sail quietly down stream, their wings 

 gently quivering the while, presumably preparing 

 for the great adventure. The voyage is fraught 

 with danger from the hungry mouths below ; but 

 always some escape all perils and rise into the air. 



Naturally the duns are always borne down by 

 the current. Why, therefore, does not the lowest 

 pool of the river, the loch or the sea, in time receive 

 all the flies and consequently also their myriads of 

 eggs ? We have often thought of this problem 

 and frequently have determined to note the progress 

 of the flies down the stream and the subsequent 

 behaviour of those that survived the dangers; 

 but the sound or glimpse of the rising trout has 

 invariably succeeded in diverting our attention 

 from the flies to the spreading rings. The flies 

 must, when they do take wing, head upstream, or 

 our rivers would be without a single representative 

 of the Ephemeridce. 



The dun has not yet attained to completion. It 

 has still to suffer or enjoy another transformation. 

 Alighting on some convenient spot, the insect 

 withdraws from its already beautiful form an 

 infinitely more delicate model of itself even to the 

 filmy iridescent wings and tender setae. It is then 

 termed a spinner or imago, the perfected fly. The 

 pale watery duns, which in their thousands throng 

 our lochs and reservoirs on quiet, still evenings of 



