paddles, but are gills. Of these one part have whisks at the tail,
and swim freely. They will change into ephemerae, cock-winged
'duns,' with long whisked tails. The larvae of the famous green
drake (Ephemera vulgata) are like these: but we shall not find them.
They are all changed by now into the perfect fly; and if not, they
burrow about the banks, and haunt the crayfish-holes, and are not
easily found.

Some, again, have the gills on their sides larger and broader, and no
whisks at the tail. These are the larvae of Sialis, the black alder,
Lord Stowell's fly, shorm fly, hunch-back of the Welsh, with which we
have caught our best fish to-day.

And here is one of a delicate yellow-green, whose tail is furnished
with three broad paddle-blades. These, I believe, are gills again.
The larva is probably that of the Yellow Sally--Chrysoperla viridis--
a famous fly on hot days in May and June. Among the pebbles there,
below the fall, we should have found, a month since, a similar but
much larger grub, with two paddles at his tail. He is the 'creeper'
of the northern streams, and changes to the great crawling stone fly
(May-fly of Tweed), Perla bicaudata, an ugly creature, which runs on
stones and posts, and kills right well on stormy days, when he is
beaten into the stream.

There. Now we have the larvae of the four great trout-fly families,
Phryganeae, Ephemerae, Sialidae, Perlidae; so you have no excuse for
telling--as not only Cockneys, but really good sportsmen who write on
fishing, have done--such fibs as that the green drake comes out of a
caddis-bait, or giving such vague generalities as, 'this fly comes
from a water-larva.'