356 SALMON AND TROUT. 



performed at various times, and many microscopic examina- 

 tions of the larvae in various stages of preparation and mount- 

 ing, have failed to bring to light anything beyond semi-digested 

 vegetable and earthy matter. Yet the formidable mandibles of 

 the larvae and the other fully developed mouth organs seem 

 eminently fitted to deal with living larvae or insects, although 

 Pictet throws doubt on this use for the mandibles, as he dis- 

 tinctly states, when speaking of the galleries in the mud in 

 which the larvae live ' Elles fouissent avec leurs mandibules 

 et leurs pattes antrieures, un peu semblables a celles des 

 courtilieres.' 



The nymph having now arrived at the period of its exist- 

 ence when it is on the point of undergoing the metamorphosis 

 from larva to subimago, is worthy of careful examination. It 

 has at this stage, when viewed under the microscope, a very 

 curious appearance. The outline of the nymph itself is un- 

 changed, but the entire margin, whether of body, legs, or setae, 

 has a semi-transparent appearance, within which is seen a dark 

 opaque insect, very similar in contour to the nymph itself, but 

 more slender in all its proportions, The head with the antennae 

 and eyes, the thorax and legs, the abdomen and setae, are each 

 distinctly visible within the corresponding organ of the nymph ; 

 and the wings are neatly folded up and packed inside the wing- 

 covers. 



Submerged about an inch under the mud, generally among 

 the roots of the weeds, the nymph works its way out of the 

 soil and rises in a series of jerks to the surface of the water. 

 On arrival there, under normal circumstances, the larval skin 

 is split longitudinally up the back of the thorax by a violent 

 effort ; through this aperture the thorax of the subimago first 

 protrudes, followed by the head ; next the legs struggle out ; the 

 abdomen and setae are then drawn out, and lastly the wings 

 emerge one after the other from the wing-covers, and are un- 

 folded and extended. The subimago remains a few moments 

 floating on the surface of the water, or supported on the nymph- 

 shuck, until the wings are dry, and then, as the Green Drake, 



