6 THE STUDY OF ANIMAL LIFE CHAP. 



years the Challenger explorers cruised over 68,900 nautical 

 miles, reached with the long arm of the dredge to depths 

 equal to reversed Himalayas, raised sunken treasures of 

 life from over 300 stations, and brought home spoils 

 which for about twenty years kept the savants of Europe 

 busily at work, the results, under Sir John Murray's 

 editorship, forming a library of about forty huge volumes. 

 The discovery of this new and strange world not only 

 yielded rich treasures of knowledge, but raised a wide- 

 spread enthusiasm for ocean-exploring which has not 

 since died away. 



We are at present mainly interested in the general 

 picture which the results of these deep-sea explorations 

 present, of a thickly-peopled region far removed from 

 direct observation, sometimes three to six miles beneath 

 the surface a world of darkness relieved only by the 

 living lamps of phosphorescence, of silent calm in which 

 animals grow into quaint forms, of great uniformity 

 throughout wide areas, and moreover a cold and plant- 

 less world in which the animals have it all their own way, 

 feeding on their neighbours, and ultimately upon the 

 small organisms which in dying sink gently from the 

 surface like snowflakes through the air. 



Far otherwise is it on the shore sunlight and freshen- 

 ing waves, continual changes of time and tide, abundant 

 plants, crowds of animals, and a scrimmage for food. 

 The shore is one of the great battlefields of life on which, 

 through campaign after campaign, animals have shar- 

 pened one another's wits. It has been for untold ages a 

 great school. 



Leaving the sea-shore, the student might naturally 

 seek to trace a migration of animals from sea to estuary, 

 and from the brackish water to river and lake ; and 

 this path has been followed by some animals. In other 

 cases, however, shallow continental seas have been con- 

 verted into freshwater lakes, and some of the originally 

 marine inhabitants have been transformed into fresh- 

 water species. In other cases accumulations of fresh 

 water have been formed apart from any seas, and these 

 have been in great part stocked by aquatic birds which 



