ast, Willy, for that's a good
one. Bring him up carefully to the side; hold your rod erect; play him
a little, for he is full of vigour. There! well done; I have got him
in the landing net. Is not he a beauty? A pound weight, I'll be bound;
and what condition! His flesh will be almost as pink as that of a
salmon. Further down stream I managed to take a fish in very different
condition; I took him where the river was rather muddy, and flowed
very slowly. Just look at him, with a body lean and dark coloured, and
an enormous head for so slender a body. "Oh! but, papa," said Willy,
"what are these curious creatures crawling over him? Do look." Ah! I
know them well; anglers call them trout lice. I will scrape off a
specimen, and put him in the bottle. Now look at him. The body is
nearly round, and almost transparent; colour rather green; it has four
pairs of swimming feet, each pair beset with a fringe of hairs; a pair
of foot-jaws; a small half-cleft tail; and a pair of fleshy circular
suckers just in front of the foot-jaws, by means of which the little
creature is able to attach itself, as a parasite, upon various fish.
It is a graceful little creature, and, as you see, can swim with great
activity in the water; now it swims in a straight line, now it
suddenly turns quickly round and turns over and over. It is known to
naturalists under the name of _Argulus foliaceus_; I do not think it
has any English name. It is found on many kinds of fish, and generally
in greater abundance upon individuals that are in an unhealthy state;
though these parasites often attach themselves to fish in good
condition. The mouth is furnished with a long, sharp sucking-tube, by
means of which the animal can pierce the skin of the fish it lives
upon, and suck up the juices. We will take a few home, and I will show
you the different parts of the creature under the microscope.

[Illustration: PARASITE (_Argulus foliaceus_) ON TROUT, NAT. SIZE AND
MAGNIFIED.]

Let us now sit down and rest for an hour, and eat our lunch; the fish
do not rise as freely as they did; perhaps later on they will be in
the humour again. But what do I see sticking to the sides of that rail
across the river; I must go and see. Well, really this is an
interesting thing. An immense mass of flies, a few alive, but the
greater number quite dead; and, look! a quantity of white eggs
underneath them. Let us examine a fly; it is of a brown or tawny
colour, and has rather long, div