SWIMMING ANIMALS 



87 



coasts of Europe, a very remarkable change comes over 

 them. From their leaf-like shape they gradually assume a 

 true eel-like appearance, becoming narrower, rounder, and 

 at the same time slightly shorter in length. After this 

 change has taken place they are the typical little eels, 

 known as " elvers," that ascend some of our rivers in such 

 countbss numbers. Here they remain in fresh water, 

 feeding and growing. After a course of time, that may vary 



Fig. 13. — Distribution of larvae (dotted area) and of adults (black stripes along coasts 

 where species occurs) of the European Eel. The contours show the limits of occur- 

 rence of the different sizes, i.e. larvae less than ten millimetres long have only been 

 found inside the ten millimetre curve, u.l. is the limit of occurrence of unmetamor- 

 phosed larvae (after Schmidt). 



from five to twenty years, the eei puts on its silver spawning 

 dress and once more sets out on the return journey to that 

 deep part of the Atlantic where it spawns and probably dies. 

 There is in America an eel which is very similar in appear- 

 ance to the common European fresh -water eel, only differing 

 in certain minute anatomical details. This eel undergoes 



