MIGRATION OF ANIMALS. 287 



geese, which follow the shoal to prey upon the herrings. 

 But, when the main body arrives, its breadth and depth are 

 so great as to change the appearance of the ocean itself. 

 The shoal is generally divided into columns of five or six 

 miles in length, and three or four in breadth. Their progres- 

 sive motion creates a kind of rippling or small undulations in 

 the water. They sometimes sink and disappear for ten or 

 fifteen minutes, and then rise again toward the surface. 

 When the sun shines, a variety of splendid and beautiful 

 colors are reflected from their bodies. In their progress 

 eouthward, the first interruption they meet with is from the 

 Shetland Islands. Here the shoal divides into two branches. 

 One branch skirts the eastern, and the other the western 

 shores of Great Britain, and fill every bay and creek with 

 their numbers. Those which proceed to the west from Shet- 

 land, after visiting the Hebrides, where the great fishery is 

 carried on, move on till they are again interrupted by the 

 north of Ireland, which obliges them to divide a second time 

 One division takes to the west, where they are scarcely per- 

 ceived, being soon lost in the immensity of the Atlantic 

 Ocean. The other division goes into the Irish Sea, and 

 affords nourishment to many thousands of the human race. 

 The chief object of herrings migrating southward is to deposit 

 their spawn in warmer and more shallow seas than those of 

 the frigid zone. This instinct seems not to be prompted by 

 a scarcity of food ; for, when they arrive upon our coasts, 

 they are fat and in fine condition ; but, when returning to the 

 | ocean, they are weak and emaciated. They continue in per- 

 j fection from the end of June to the beginning of winter, when 

 I they begin to deposit their spawn. The great stations of the 

 | herring fisheries are off the Shetland and the Western Islands, 

 and along the coast of Norfolk. 



Beside salmons and herrings, there are many fishes which 



j observe a regular migration, as mackerels, lampreys, pilchards, 



| &c. About the middle of July, the pilchards, which are a 



species of herrings, though smaller, appear in vast shoals off 



;! the coasts of Cornwall. When winter approaches, like the 



' herrings, they retire to trie Arctic seas. Though so nearly 



!j allied to the herring, it is not incurious to remark, that the 



1 pilchards, in their migration for the purpose of spawning, 



choose a warmer latitude. 



Of the land-crab there are several species. The migration 

 of what is called the violet land-crab deserves some notice. 

 It inhabits the warmer regions of Europe, but its particular 



