CHAPTER VII.

Geographical Distribution and Migrations of Fish.

ALTHOUGH we are less acquainted with the habitations of marine animals than with 
the grouping of the terrestrial species before described, yet it is well 
ascertained that their distribution is governed by the same general laws. The 
testimony borne by MM. Péron and Lesueur to this important fact is remarkably 
strong. These eminent naturalists, after collecting and describing many thousand 
species which they brought to Europe from the southern hemisphere, insist most 
emphatically on their distinctness from those north of the equator ; and this 
remark they extend to animals of all classes, from those of a more simple to 
those of a more complex organization, from the sponges and medusæ to the 
cetacea. “Among all those which we have been able to examine,” say they, “with 
our own eyes, or with regard to which it has appeared to us possible to 
pronounce with certainty, there is not a single animal of the southern regions 
which is not distinguished by essential characters from the analogous species in 
the northern sea *.
 

The fish of the Arabian gulf are said to differ entirely from

* Sur les Habitations des Animaux Marins. Ann. du Mus. tom. xv., cited by 
Prichard, Phys. Hist. of Mankind, vol. i, p. 51.