52 NATURALIST'S CABINET. 



Supposed causes of their migrations. 



The more immediate cause of migration is vari- 

 ously accounted for. Leuwenhoeck says, that 

 the Channel every year teems with an innumer- 

 able quantity of worms and little fish, on which 

 the herrings feed ; that they are a kind of manna, 

 which these fish come punctually to gather up ; 

 and when they have entirely cleared the seas in. 

 the northern parts of Europe, they descend to- 

 wards the south, where they are invited by a new 

 stock of provisions. Anderson is of opinion, that 

 they would never depart from their most desi- 

 rable retreat in their icy, northern entrenchments, 

 did not their numbers render it necessary for 

 them to migrate ; and as with bees from a hive, 

 they are compelled to seek for other retreats. 



Another opinion is, that they remove for the 

 sake of depositing, their spawn in warmer seas, 

 that will mature and vivify it more assuredly 

 than those of the frozen zone. 



Respecting the manner of migration, a cele- 

 brated naturalist says, " the herrings being fright- 

 ened by the numerous enemies which pursue 

 them, retire to the Arctic ocean, where those 

 enemies cannot live beneath the ice for want of 

 air. But as they multiply prodigiously in that 

 sea, they are obliged, by the scarcity of food, to 

 send off colonies at the beginning of every year. 

 These colonies, after clearing the ice, extend in 

 a vast body some hundred miles in breadth ; but 

 meeting with numerous enemies by the way, 

 they are attacked, dispersed, and separate ii 



