EPHEMERID/E OF THE CHALK STRK \M s. 7 



of the nymph's career, becoming less and less frequent as he 

 advances towards adult proportions. In due course what are 

 known as the wing-cases gradually begin to make their 

 appearance upon his back, and with the full development of 

 these the nymph begins to prepare for his next change. 



At this stage he becomes more restless and active than 

 ever before, making short excursions from time to time in an 

 upward direction, until finally, having made up his mind that 

 the time is ripe, he thrusts his thorax well above the surface 

 of the water. Immediately it splits down the centre, and 

 from the shell of what was once the nymph, the dainty little 

 dun or subimago quickly disengages itself, leaving the empty 

 shuck either to go its own way down the stream or to serve as 

 a raft for its late tenant. 



(iii) The Subimago or Dun, whilst newly hatched and 

 floating down the surface of the stream, has arrived at that 

 period of its career at which it is most interesting to the majority 

 of fishers, though it has not yet reached the final stage of its 

 development. Soon it rises from the water and makes its way 

 to the shelter of a friendly bush where it remains for some 

 twenty-four hours or so, probably hidden on the under side of 

 a leaf, until the time is ripe for the final change. For the last 

 time the skin of the thorax splits and the perfect insect with- 

 draws itself from the subimaginal covering, leaving the envelope 

 still attached to the last resting place of its owner. This 

 envelope, of course, bears the exact outline of the dun, with 

 the exception of the wing cases, which gently subside as they 

 are not sufficiently stiff to maintain their erect position. 



(iv) The Imago or Spinner is endowed with much more 

 energy and activity than the Dun. It is perfect in all the 

 parts necessary to its existence and its development is complete. 



The Spinner is equipped with no machinery for taking 

 nourishment of any kind, so that its strength is spent in the 

 course of a few days, though its life is by no means so ephemeral 

 as is commonly supposed. The one duty remaining to the 

 Spinners is the reproduction of the species. After the eggs have 



