Page:British Reptiles, Amphibians, and Fresh-water Fishes.djvu/72

BRITISH FRESH-WATER FISHES dorsal. The tail bears the caudal fin. On the lower part of the body there is the pectoral fin behind the hind portion of the gill-covers, the ventral fin is right at the base of the belly, and the anal fin is situate where the body perceptibly narrows towards the tail. The position of these fins varies in certain kinds of fishes, and this will be referred to when we are considering our own fresh-water species individually, but it will be as well to set out the uses of the fins just described. I have not read a better account of these than appears in one of Mr. W. J. Gordon's useful Handbooks, and I feel sure he will allow me to repeat what he has written in his excellent book "Our Country's Fishes." Mr. Gordon says: "The caudal fin is the fish's main propeller, with the paired fins he retains his trim, and the dorsal and anal he uses as a keel to keep him straight on his course. With his tail he does most of his steering, but he brings in his pectorals to help him. A stroke of the tail to starboard and a stroke or two with the starboard pectoral, with the port pectoral held against the body, sends his head to port; a stroke of the tail to port with a stroke or two of the port pectoral, and the starboard pectoral held in, sends him round to starboard; in fact the pectoral thrown out of action serves as a pivot on which he turns. Cut off a pectoral and he falls on the opposite side; cut off both and his head sinks; cut off all his fins and he capsizes, owing to his upper half being the heavier."

Some fishes have the eyes to the left, others to the right. 56