EELS 



295 



whence they never return. The fry are transparent creatures known as 

 Leptocephali. Apparently the breeding-resort of the eels of northern Europe 

 is in deep water outside the 500-fathom line to the south-west of Ireland, where 

 their Leptocephali have been taken in abundance. It by no means follows that 

 all north European eels which reach the sea arrive at the breeding-area, and 

 possibly Finnish eels never breed at all. If this be so, it is practically certain 

 that young eels, or elvers — unlike young salmon — do not return to the rivers 

 from which their parents started ; this being improbable, seeing that eels are 

 hatched in the sea. 



Naturalists are still in ignorance with regard to the age of the youngest 

 Leptocephalus larva at present known, namely, specimens of about 7 cm. in 



HAMMER-HEADED SHARK. 



length, it being uncertain whether these are six or eighteen months old. Of 

 younger larvae and the eggs nothing is known, and we are also ignorant as to the 

 interval which elapses between the arrival of eels in the sea and their spawning. 

 Neither is it known what becomes of eels subsequent to spawning ; possibly 

 they die soon after this event, although they may live for a considerable period. 

 All that is definitely known is that after having once entered the sea they never 

 return to fresh water. 



In Sweden, as the result of recent investigations it has been found that the great 

 majority of the five-year-old eels collect at the mouths of the rivers discharging 

 into the Gottland and Botten lakes, where they remain in a barren condition from 

 five to seven years, after which they make their way, as ten- to twelve-year-old 

 fishes, by the Kattegat, the Skagerak, and the North Sea to the Atlantic for the 

 purpose of spawning. 



