DISTRIBUTION OF ANIMALS. 



577 



their presence is considered to be the principal cause of the absence of fish in the pools of 

 the Llanos. All the inhabitants of the waters avoid them, and it became necessary to change 

 the direction of a road near Uritico, in consequence of the number of mules lost in 

 fording a river in which they were very numerous. It is supposed that they can 

 communicate their electric shock through a thick mass of water, and kill from a distance 

 the prey they are anxious to devour. 



From the facts gathered with reference to fishes, it appears that particular districts or 

 basins of the ocean have tribes peculiar to them, distinct from those which inhabit even 

 contiguous seas. Thus the species common to the Arabian Gulf are said to differ 

 entirely from those of the Mediterranean, and according to MM. Seron andLeseur, there 

 is not a single animal of the southern regions which is not distinguished by essential 

 characters from the analogous species in the northern seas. The flying-fish are chiefly 

 intertropical, or, at the farthest, they are never found beyond the fortieth parallel of lati- 

 tude, while the Atlantic species differ from those of the Pacific. The cod-fish, diffused 

 throughout the whole of the northern ocean between Europe and America, chiefly haunt 

 the great banks of sand to the south-east of Newfoundland, where they exist in 

 undiminished numbers owing to their astonishing fecundity, which makes up for the havoc 

 occasioned by the extensive fisheries. Leeuwenhoek counted more than nine millions of 

 eggs in the ovary of a cod-fish of the middle size. While many species of fish appear 

 never to depart from the site of their birth, but live and die in the same spot, others 

 periodically migrate to a vast distance for various purposes, and become the food of 

 nations in whose seas they are strangers and foreigners. This is the case with the 

 mackerel of the north of Europe, the thunny of the Mediterranean, the pilchard, and the 

 herring. The latter, so eminently important in a commercial point of view, derives its 

 name from the German heer, an army, in allusion to the countless swarms that annually 

 come up from the depths of the arctic sea, and proceed to the western shores of Europe, 

 to the coasts of the United States, as well as to those of Kamschatka, and the neighbour- 

 ing islands. The herrings migrate to find food, and to deposit their spawn, forming shoals 

 consisting of millions upon millions, several miles in length and width, and many fathoms 

 in thickness. The water ripples before them as they advance. The sea-birds hover over 



