Ah! here is a capital place. Now, Master Willy, there is no tree to interfere with your throw, so cast in just near that spot, quietly, carefully, anxiously; if there is a fish there he cannot resist your green drake. I recommend him the artificial before the fat natural fly. As Christopher North says--"Devouring ephemerals! Can you not suffer the poor insects to sport out their day? They must be insipid eating--but here are some savoury exceedingly ... they carry _sauce piquante_ in their tails. Do try the taste of this bobber--but any of the three you please." There, hold fast, 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.]