CHAPTER FIFTY-EIGHT 



The sea the 





Marine and 

 terrestrial 

 life con- 

 trasted 



LIFE IN THE SEA 



1. THE sea occupies the greater part of the world's 

 sur f acej an j teems with varied forms of life. The 

 oldest known fossils appear to be exclusively marine, 

 but these have gone far along the path of evolution. 

 The beginnings of life were certainly associated with 

 water, but they may have been in the soil, which is 

 still occupied by a great variety of organisms scarcely 

 known even to naturalists. However this may have 

 been, the sea is nevertheless the great mother of life, 

 the source of many great groups, some of which have 

 emerged from the waters to occupy the land. The 

 reverse process, the adaptation of land groups to marine 

 existence, is much less common. The whales and 

 porpoises are mammals, certainly with terrestrial 

 ancestors. A few species of mollusks, living near the 

 shore, show characters indicating their relationship 

 to land snails. Some true snakes, not the sea serpents 

 of fable, are sea dwellers. There are hemipterous 

 insects which skim the surface of the open ocean, but 

 are related to inland forms. All such instances, 

 taken together, are relatively few, whereas the whole 

 arthropod phylum, for example, appears to have first 

 developed in the sea. 



2. There is, however, the strongest contrast between 

 the character and evolution of marine and terrestrial 

 life. In particular, the plant and animal kingdoms 

 occupy very different relative positions. At first sight 

 it might well appear that the sea is the home of animals, 

 the land of plants. Plant life in the sea consists almost 

 wholly of lowly forms, sometimes gigantic, as the 

 kelp of the Pacific coast, but flowerless and anything 



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