CHAP. VIII. MIGRATION OP INSECTS. 263 



fish lives in the same latitudes all the year ; and that 

 the cause of these immense shoals is simply that the 

 fish, during particular seasons, come near the coast, 

 where they then appear in vast multitudes. 



(277.) The tunny (fig. 74.), in like manner, enters 

 the Mediterranean about the vernal equinox, for the 

 purpose of spawning ; it swims in large companies, 

 arranged, as it has been said, in a triangular phalanx, 

 like the geese and other birds, the point of which acts 



74 



like a rudder to cut through the opposing waters, while 

 a broad base is presented to those tides and currents 

 which must occasionally be encountered. On their re- 

 turn, they approach the coasts of Africa, and the young 

 fish are placed in the van of the squadron. 



(278.) The migrations of many tribes in the INSECT 

 world unfold to the observer of nature a fresh subject 

 of contemplation. These associations are chiefly oc- 

 casioned from two different motives ; they are either 

 for the purposes of procuring food, or for establishing 

 a new colony when the parent society has increased 

 beyond its due limits. The former of these migrations 

 is much more remarkable than the latter, and is ex- 

 emplified, in the most striking and terrible manner, by 

 the family of locusts, whose assembled myriads darken 

 the sun, and desolate kingdoms. Interesting as is the 

 history of these formidable creatures, we must at pre- 

 sent confine our attention to those circumstances only 

 which regard their association and migration. This 

 numerous family, of which the common grasshopper is 

 a small but excellent example, is spread over all tem- 

 R 4 



