22 MIGRATIONS OF FISH. 



ginous envelope, and are fertilized after they are laid. Some of 

 these animals are, on the contrary, ovo- viviparous ; but whatever 

 may be the manner in which the young fish are brought into 

 life, they are from the moment of their birth completely aban- 

 doned to themselves, and many of them perish during the early 

 period of their existence. There are a few species, however, 

 such as the Gobies, which make regular nests for their young, 

 composed of sea-weed ; and tend them with great care, 



545. It is to the simultaneous development of an incalculable 

 number of eggs deposited in the same place, and to the instinct 

 which induces different fish to follow each other, that we are to 

 attribute the union of certain species in immense and closely- 

 packed legions, called by fishermen shoals offish. We can hardly 

 term these unions, societies ; the individuals of which they are 

 composed do not assist one another ; the same wants to be satis- 

 fied keep them in the same locality, or remove them from it ; 

 and if we see them occasionally following an individual as a 

 guide, it is probably the consequence of a tendency to imitation, 

 which always accompanies the first dawnings of intelligence. 



546. However it may be, these animals, thus united in 

 troops, often make long journeys, sometimes to gain the sea, 

 sometimes to ascend rivers or to change their climate. Certain 

 fish lead an almost sedentary life, and remain always in the 

 locality where they were produced ; others are always wander- 

 ing, and a great number of these animals periodically make 

 journeys of greater or less length. At the time for spawning, 

 they generally approach the coasts or enter the rivers ; and in 

 this manner they sometimes effect an extremely long passage. 

 Every year, towards the same period, large numbers of migrat- 

 ing fish arrive in the same places ; and it is generally believed 

 that several of these species regularly migrate from the north 

 towards the south, and from the south towards the north, fol- 

 lowing a determined route ; but perhaps it would be more true 

 to believe, that when they disappear from the shores, they only 

 retire into the greater depths of the sea. The Herring is one 

 of the most remarkable fishes in this respect, as well as the most 

 celebrated on account of the importance of the fisheries of which 



