SCIENCE AND PHILOSOPHY 149 



vivid one the Migration of Eels, which has 

 been recently discussed in this connection by 

 Mr. E. S. Russell ("Vitalism," Rivista di Scienza, 

 April, 1911). It is a useful case, because the ani- 

 mal has a brain of a very low order, and we are 

 not warranted in using in regard to it the psycho- 

 logical terms which are indispensable in the case 

 of the more intelligent birds and mammals. 



The eels of the whole of northern Europe prob- 

 ably begin their life below the 500-fathom line on 

 the verge of the Deep Sea away to the west of 

 Ireland and southward on the verge of the dark, 

 cold, calm, silent, plantless world of the abysses. 

 The young eel develops and starts in life, and 

 feeds and grows far below the surface, but the 

 early chapters of the life-history are still quite 

 obscure, and do not at present concern us. It 

 rises to the upper sunlit waters as a transparent, 

 sideways flattened, knife-blade-like larva, about 

 three inches in length, with no spot of colour 

 except in its eyes. It lives for many months in 

 this state known as a Leptocephalus expending 

 energy in gentle swimming, but taking no food. 

 It subsists on itself, and becomes shorter and 

 lighter, and cylindrical instead of flat. It is 

 gradually transformed into a glass-eel, about two 

 and a half inches long, like a knitting-needle in 

 girth. It moves towards the shores. After about 

 a year it is one of a million elvers passing up one 



