1895 THE MICROSCOPE. 115 



The Cycloid. — The scales are so called because of 

 their roundish form and because much of their surface 

 when magnified is seen to be covered with concentric 

 lines. At the top, where they are attached to the body, 

 these concentric lines are divided by radial lines, some- 

 times making slight, sometimes deep undulations in the 

 surface of the scale. To this order belong the Salmon, 

 E,oach, Grold-flsh, Silver-fish, Cod-fish, Minnow, Carp (fig. 

 2), Herring (fig. 5), Blue-fish (fig. 6), Eel (fig. 3), and 

 others. 



Along the side of most fishes is a line known as the 

 lateral line, which is formed by a kind of scale usually 

 more horny than the others and pierced by a tubular ori- 

 fice having an opening on the upper side near the outer 

 edge and another opening on the under side where it is 

 attached to the body (fig. 7, Salt-water Perch, 5 diam.). 

 In fig. 2, Grerman Carp (2 diam.), this tube divides just 

 above the exposed part, thus having two openings on the 

 under side. It has been supposed that this tube was for 

 the escape of a mucous substance whicli was poured out 

 from glands beneath, to protect the skin from the mas- 

 cerating influence of the water and to diminish the fric- 

 tion in swimming, but this has been denied. 



By carefully detaching a scale from a bright colored 

 fish of this order, and examining the under side of the 

 part which is exposed, we find a layer of soft substance 

 corresponding in color to the color of the first. Remove 

 a little of this to a slide, and by examining it with a 

 power of 300 diameters, we shall find that it consists of 

 two substances. One is a layer of loose membraneous 

 cells containing coloring matter. These lengthened cyl- 

 indrical cells are arranged side by side and run at right 

 angles to the lateral line. Now, if a small drop of water 

 be added to this mass and it be gently agitated with the 

 point of a needle, the water around will be seen to be 

 full of minute flat spicules or crystals, varying in size 



