COLOUR, FORM, AND MOVEMENT. 73 



those which are open. The air bladder is probably of 

 use in the longer migrations, when it may help to keep 

 the fish relatively at the same depth in the course of the 

 journey. 



Throughout, the attempt should be made to maintain 

 this lesson on observational lines, by, as has been suggested, 

 close watching of the different movements made by the 

 fins, and noting the result of these movements ; 



e.g. raising and lowering of median body fins ; 

 action of tail fin ; 

 action of paired fins, together and separately. 



MIGRATIONS OF THE COMMON EELS. 



As a particular illustration of the powers of fishes, the lessons on 

 the swimming fish might be followed by the teacher recounting the 

 outstanding facts narrated below regarding one of the most familiar 

 of fishes occurring in fresh waters. 



Until a few years ago it was necessary in speaking of the 

 life-history of the common eel to refer to it as a mystery. 

 To-day much of the mystery has been removed, and in its 

 place we have a tale of remarkable interest. 



The " march of the elvers " or young eels up the rivers 

 from the sea in the spring or early summer has long been 

 an event of interest and wonder. It is an event to be 

 looked for by those within reach of the banks of a river or 

 smaller stream. The time varies with the stream, but in 

 general it is later in the south than in the north. 



The young eels on leaving the sea spend their time in 

 the fresh water, feeding and growing, sometimes leaving 

 the water and crossing the fields to another stream ; in 

 this way they live for about four or five. years, when a 

 return migration down the streams to the sea takes place. 



It is a matter of some importance to note that eels at 

 this later stage have assumed a different appearance from 

 the ordinary. They present a silvery metallic appearance. 

 Their eyes are larger and are placed closer to the top of the 

 head; their sense of smell has become more acute, as is 



