THE OCEAN AND THE LANT) 197 



a large and ugly amphipod an inch or so in length, entirely 

 transparent, though quite as tough as any other. 



From the surface of the ocean down to great depths animals 

 exist, the number of major groups and of species rapidly de- 

 creasing and the size becoming more nearly uniform below the 

 Umit of light until in the deeper layers only grotesque fishes, 

 cuttle-fishes, jelly-fishes, crustaceans, nemerteans and echino- 

 derms, are found, all feeding on each other. 



A comparison of the animals living in the sea with those in- 

 habiting the land brings out at once a most extraordinary para- 

 dox. 



About three-fourths of all known kinds of animals live on 

 the land; but this formidable array represents only a few of 

 the major types. The most numerous land creatures are the 

 insects, of about half a milhon sorts. Equal in importance, 

 much larger, but much fewer both in kinds and numbers, are 

 the vertebrates. Next in significance are the molluscs and the 

 nematodes. Of much less importance are the annelids, includ- 

 ing earth-worms, land leeches, and onychophores. The repre- 

 sentatives of the other major types found on the land, plana- 

 rians and nemerteans, are not of much importance in the 

 picture as a whole. 



While in the sea there live less than one-fourth of all the 

 animals that so far have been described, these are widely dis- 

 tributed among about three times as many major types as are 

 those inhabiting the land. Certain marine types, like sponges, 

 coelenterates and polyzoans, and some groups of annehds, are 

 sparsely represented in fresh water, which also has some t>'pes, 

 like gastrotrichas and the rotifers, quite or almost wholly re- 

 stricted to it. But of the major types of animals no less than 

 ten (priapulids, sipunculids, phoronids, brachiopods, chaetog- 

 naths, echinoderms, enteropneusts, tunicates and cephalo- 

 chordates), nearly half again as many as all land-living types 

 together, are exclusively marine. 



On land different locaUties and situations are extremely 

 variable as regards the physical conditions. We find hot, tern- 



