REPORT OF COMMISSIONERS OF INLAND FISHERIES. 49 



the two adult forms so that there is httle doubt that Eigenmann's 

 identification of Leptocephalus grassi with the American eel is correct. 



Very recently, 1906 and 1908, important additions to our knowl- 

 edge of the life history of the eel have been made. These have 

 thrown a great deal of light on questions relating to the time and 

 place of its spawning, its migration, the physical and biological 

 conditions of its environment, as well as its development and rate of 

 growth. This recent work we owe to the Danish investigators 

 Schmidt, Petersen, and Gemzoe, working under the auspices of the 

 International Council for the Exploration of the Sea. 



In the present condition of our knowledge regarding the eel there 

 still remain certain rather considerable gaps — for instance, nothing 

 is known of the seaward migration of the eel after it leaves the coast; 

 also its appearance at sexual maturity, the ripe eggs, and the earliest 

 larval stages in the case of the common eel are alike unknown. Yet 

 in spite of these obvious deficiencies, investigation has been carried 

 far enough to leave no room for doubt regarding its main features, and 

 it is now possible to give a connected and quite detailed account of 

 the most important events in the biography of the eel. 



It has long been a matter of common knowledge that in late 

 autumn great numbers of adult fresh-water eels of large size and 

 bright silvery sheen set out on a migration down the rivers toward 

 the sea. This migration has been observed in all the rivers of north- 

 western Europe, especially on the continent, where it is responsible 

 for an important eel fishery. In this country, this autumnal hegira 

 toward the sea has been observed in most of our rivers, and, in fact, 

 it has at times attracted considerable public notice because in many 

 cases the migrating eels have crowded down the rivers in such multi- 

 tudes as to fill the sluiceways, choke up the mill-wheels, and thus to 

 cause a temporary shutdown. The connection of this conspicuous 

 phenomenon with the other known facts in the life history of the eel 

 has never been entirely clear until recently. What becomes of the 

 eels after leaving the fresh water had long been a mystery. The 

 Danish naturalists, however, have been able to secure certain direct 



