has its own pattern of scale, and that you could tell a species of fish by its scales?
The paper showed that the scales of fishes were composed of the same material, chitine, as the feathers of birds, or the hair and nails of animals—a kind of substance only found in the animal kingdom, and never in the vegetable; that these scales are developed in little pockets in the fish's skin, which you can plainly see for yourself when a herring is scaled. They are arranged all over the fish's body like the tiles covering a roof, partly over-lapping each other, as is seen by one part of the scale being often 
Fig. 12.—Scale of Pike. different from the other.
Jack looked through the microscope and was delighted. He was always a reverent-minded boy, and the sight broke on his mind like a new revelation. How exquisitely chaste and beautiful were the markings, lines, dots, and other peculiarities I Then the scales which run along the middle line of the fish were shown him, and theducts perforating them, out of which the mucus flows to anoint the fish's body, and thus reduce the friction of its rapid movement through the water. The lad was half bewildered at the possibility of the new knowledge. "Could anybody get to know about these things?" he asked Willie, who told him of course he could, if he would only take a little trouble.
"But," said his young friend, "I would advise you to get a pocket-magnifier first, and begin to examine with that. Some fellows begin right off with a powerful microscope they get their governors to buy them, and they work it like mad for a month or two, and then get tired of it. Fact is, they never learned the art of observing."
"What do you mean by that?" said Jack.
"Why, getting into the habit of looking about you, keeping your eyes open, and quickly spotting anything unusual. Fancy a fellow beginning to use magnifying glasses of thousands of times
