42 THE BIOLOGY OF THE SEASONS 



being on a belt running from north to south along the 

 continental slope towards the eastern part of the Atlantic 

 depths. 



The " mystery of the eel " has engaged the attention of 

 many naturalists, who have contributed to our present- 

 day approximation to a solution. The biggest contribu- 

 tions are four, (a) In 1880, Jacoby proved that eels 

 remained barren in fresh water, and suggested that the 

 sexual maturity was not attained until they had gone 

 far out into deep water, (b) About 1896, Grassi and 

 Calandruccio concluded, from their observations in the 

 Mediterranean, that the eel matures in deep water, where 

 its eyes become larger ; that it spawns in deep water, where 

 its eggs float ; that the development includes a meta- 

 morphosis, and that the larval form is the peculiar trans- 

 parent pelagic creature which had been called Leptocephalus 

 brevirostris. They found these in considerable numbers in 

 the deep water of the Straits of Messina, (c) About 1906, 

 Schmid found numerous specimens of this Leptocephalus 

 along a belt from the Faroes southwards, described the 

 metamorphosis into the " glass-eel " stage, and brought 

 forward evidence of a migration shorewards during the 

 process of change, (d) Another naturalist, Petersen, also 

 deserves credit for showing that what had been called 

 " silver " eels, with a silvery coat and big eyes, are the 

 mature forms of the " yellow " eels of the ponds. They 

 put on a " wedding garment " as they are about to go 

 down to the sea. 



As neither the first nor the final chapter in the life- 

 history of the common eel is as yet known, neither the eggs 

 nor the spawning adults having been discovered, one 

 naturally asks for evidence in support of the statement that 

 has been made as to their birthplace. The evidence, which 

 we owe to the researches of Dr. Johs. Schmid, consists 



