THE AQUATIC VERTEBRATES 1041 



to ten miles from Cayuga Lake up the streams to spawn. The 

 silver lamprey of the Mississippi Valley ascends small brooks in 

 the spring. On the Pacific slope the Pacific lamprey ascends 

 streams in large numbers. At La Grange, Idaho, I found very 

 many congregated below a milldam which they had not been able 

 to ascend. The sturgeons, for the most part living in the sea, also 

 ascend streams to spawn. 



While many species of fishes have the habit of entering fresh 

 water when they approach ripeness, the eel alone, of the fishes of 

 the northern hemisphere, has the reverse habit of taking to salt 

 water when the reproductive period approaches. It has been well 

 known for many years that during winter and early spring the 

 young of the eel enter the mouths of streams in enormous numbers. 

 Redi records the entrance of young eels into the Arno in 1667, and 

 says that at Pisa three million pounds of young eels 30-120 mm. 

 were taken in five hours. They find their way for hundreds of 

 miles from the ocean. "Young individuals three to five inches 

 long ascend rivers in incredible numbers, overcoming all obstacles, 

 ascending vertical walls or floodgates, entering every large and 

 swollen tributary, and making their way even over terra firma to 

 waters shut off from all communications with rivers." 



The American eel, which is closely related to the European eel, 

 is found in all fresh waters emptying from the Gulf of St. Lawrence 

 to Mexico. Eels have been seen in Colorado 1500 miles from the 

 Gulf of Mexico, at an elevation of 7200 feet. Only the females 

 ascend such distances, the males remaining near the coast. While 

 in fresh water they feed on everything eatable. When they ap- 

 proach their full size, in about four years, they descend the streams 

 to the ocean in autumn. They are lost sight of beyond a distance 

 of a mile from shore, but about six months after they have entered 

 the sea, eel eggs have been found floating on the surface. They 

 are large eggs, with a very large perivitelline space, and vesicular 

 yolk. They hatch into larvae quite unlike eels. These become 

 gradually greatly modified, but not in the direction of becoming 

 eel-like. It is not until the larvae are about a year old that they 

 are metamorphosed into young eels which ascend streams such as 

 their parents have descended two years previously. Like all fishes, 



