MAY-FLY FISHING. 353 
varying according to the temperature; thus, in very cold 
weather it has been found burrowing more than three feet in 
the river-bed, in the early spring at a depth of about eighteen 
inches, while at the commencement of June it is only an inch or 
two below the surface. It is quite possible that this statement 
may give rise to some controversy, and instances will be given 
of these larvee being found in fast-running stickles, or shallows, 
and on hard clean gravel, and on this evidence anglers will be 
asked to discredit the careful observations of naturalists re- 
peated over and over again during the last century. There is, 
however, no doubt that some considerable number of May-fly 
larvee are from time to time found in rapid water where there 
is not sufficient mud to cover them. This seeming anomaly is, 
to my mind, quite capable of being explained. Every flood, 
every cleaning of the river, every disturbance of the mud, 
and every cutting of the weeds must of necessity set adrift a 
certain number of larvee ; these are unable to progress against 
or even across the stream, and the moment they find they are 
being carried down, instead of exhausting their strength by 
vain efforts to stem the current, they let themselves sink to the 
bottom, and crawl along until they find a suitable place, in 
which they once more commence their burrowing operations. 
Hence the occasional presence of larvae on hard gravelly 
scours; and, of course, the greater the number of May-flies on a 
river, and the more frequent the causes of disturbance, the more 
numerous are likely to be the occasions on which the larve and 
nymphs are found on what must be considered unsuitable 
ground. 
After a certain number of moults the wing-covers attached 
to the thorax become visible; at first they are transparent and 
very small, but gradually grow larger and become darker in 
colour as the development of the wings folded up within them 
progresses. From the time of the first appearance of the wing- 
covers the name zymph is applied to the immature insect, but, 
beyond that it has grown larger and slightly darker in colour, 
and that the mouth organs and branchie are further developed, 
L AA 
