356 SALMON AND TROUT. 
performed at various times, and many microscopic examina- 
tions of the larvee 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 larve and the other fully developed mouth organs seem 
eminently fitted to deal with living larve 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 larve live—‘ Elles fouissent avec leurs mandibules 
et leurs pattes antérieures, un peu semblables 4 celles des 
courtiliéres.’ 
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 sete, 
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 antenne 
and eyes, the thorax and legs, the abdomen and setz, 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 sete 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, 
