232 THE INFANCY OF ANIMALS 



But the migration is a fact, and gave rise, years ago, 

 to a heated controversy as to the method of travel. The 

 Swedish naturalist Malm was the first to study this problem, 

 and from the species which he examined he decided that 

 the eye moves outwards and upwards across the roof of the 

 head tiU it takes up a position by the side of its fellow. But 

 at about the same time — between i860 and 1870 — a Danish 

 naturalist was also tackling the problem, and he came to 

 the conclusion that the eye passed through the head ; and 

 for a long time controversy waxed furious as to which 

 was right. As a matter of fact, both were ! This was 

 proved when, in 1878, an American naturalist actually 

 kept living specimens of young flat fish, in some of which 

 the eye passed round, and in others through the head. 

 And when this apparent diversity came to be further 

 explored it was found that the passage through the head 

 was apparent, not real, and was due to the fact that in 

 such species the dorsal, or back fin, extended far 

 forwards beyond the level of the uppermost eye, and 

 that the eye of the under surface simply tunnelled 

 under the fin, and over the head. In the sole and the 

 turbot the forward growth of the fin to the snout does 

 not take place until after the undermost eye has taken 

 up its position on the upper surface of the body. 



We bring this chapter to an end with a brief account 

 of the early history of the common fresh-water eel, which 

 for long remained an apparently insoluble mystery. We 

 now know that the eels of our rivers and ponds migrate 

 to the sea to spawn, and that having done this they die. 

 No eel, whether of fresh water or of the sea, like the 

 conger, ever lives to see its offspring. Our river eel, then, 

 when the supreme period of its life is at hand, makes all 

 speed for the sea, putting on, during the journey, nuptial 



