74 COLOUR, FORM, AND MOVEMENT. 



evidenced by the greater development of the smelling organ. 

 Another sensory organ whose development is accentuated 

 is the lateral line, a structure whose function appears to 

 be of the nature of a chemical sense or to have something 

 to do with the appreciation of pressure in the water. 

 Further, there is much fat accumulated on the body, the 

 muscles are exceptionally well developed, and the breast 

 fins are increased in size. Notwithstanding these changes, 

 very suggestive of the fish being in the pink of condition, 

 the eels are not mature. 



What do these changes signify ? The eel is starting 

 upon a very long journey, upon which it does not stop to 

 feed. Many of the characters assumed are those of deep 

 sea fishes, e.g. the large eyes or well-developed lateral line. 

 The eel is in reality a deep sea fish and this migration is a 

 return to the ancestral home to spawn. 



The journey is not simply to the sea. The eels of the 

 streams and rivers of the east coast of Great Britain, for 

 example, do not spawn in the North Sea nor in the waters 

 of the Baltic. No eggs, nor young, nor mature eels have 

 ever been found there. Nor do any fully grown eels ever 

 return to the fresh waters. The spawning beds of the eels 

 of the north-west of Europe are situated in the North 

 Atlantic at one thousand fathoms depth and at least one 

 thousand miles from fresh water. 



The eels travel at the rate of eight to ten miles per day, 

 at which rate it will be seen they must spend several 

 months on the journey. By the time they reach their 

 journey's end they have become mature, and the eggs are 

 probably spawned in the spring time. From these there 

 develop after more than one larval period the elvers which 

 appear the following spring in our rivers and which there- 

 ore must be a year old. The parent eels are believed to 

 die after spawning. 



The migrations of the eel illustrate a remarkable instinct. 

 They are difficult to explain, except on the ground that the 

 migrations have been evolved in the past through changes 

 in the distribution of land and water, in which the fresh 

 waters to which the eels had betaken themselves for feed- 

 ing have through the ages been further and further removed 



