=Family Anguillidæ.=—The most primitive existing family is that of the typical eels, _Anguillidæ_, which have rudimentary scales oblong in form, and set separately in groups at right angles with one another. These fishes are found in the fresh and brackish waters of all parts of the world, excepting the Pacific coast of North America and the islands of the Pacific. In the upper Great Lakes and the upper Mississippi they are also absent unless introduced. The species usually spawn in the sea and ascend the rivers to feed. But some individuals certainly spawn in fresh water, and none go far into the sea, or where the water is entirely salt. The young eels sometimes ascend the brooks near the sea in incredible numbers, constituting what is known in England as "eel-fairs." They will pass through wet grass to surmount ordinary obstacles. Niagara Falls they cannot pass, and according to Professor Baird "in the spring and summer the visitor who enters under the sheet of water at the foot of the falls will be astonished at the enormous numbers of young eels crawling over the slippery rocks and squirming in the seething whirlpools. An estimate of hundreds of wagon-loads, as seen in the course of the perilous journey referred to, would hardly be considered excessive by those who have visited the spot at a suitable season of the year." "At other times large eels may be seen on their way down-stream, although naturally they are not as conspicuous then as are the hosts of the young on their way upstream. Nevertheless it is now a well-assured fact that the eels are catadromous, that is, that the old descend the watercourses to the salt water to spawn, and the young, at least of the female sex, ascend them to enjoy life in the fresh water." [Illustration: FIG. 101.—Common Eel, _Anguilla chrisypa_ Rafinesque. Holyoke, Mass. ] =Reproduction of the Eel.=—Dr. Gill ("Riverside Natural History," p. 103) gives the following account of the reproduction of _Anguilla_: