CHAPTER LXXVI 



LIFE IN DIFFERENT SURROUNDINGS— SHALLOW WATER, 

 DEEP WATER, AND SURFACE FAUNAS OF THE SEA 



In writing this book an attempt has been made to illustrate 

 some ot the innumerable ways in which animals have become 

 adapted to exist in various surroundings or environments. Occa- 

 sion has been taken to consider pretty fully adaptations to various 

 kinds of food, to the exigencies of life in water, on the ground, 

 in the ground, among the trees, and in the air. It may there- 

 fore perhaps suffice here to deal with a few facts having reference 

 to the adaptations which have been evolved in relation to exis- 

 tence in the sea, especially as the last chapter has been mainly 

 devoted to land animals. 



In dealing with marine forms it is found convenient to divide 

 the oceans into three zones which pass into one another, the 

 Neritic, the Abysmal, and the Pelagic, each of which is char- 

 acterized, broadly speaking, by a special fauna. The Pelagic 

 zone includes the surface waters so far as penetrated by light to 

 any marked extent; the Neritic zone extends from high-tide 

 mark to a depth of 500 fathoms; and the Abysmal zone stretches 

 from this into the deepest and gloomiest ocean abysses. 



It is further the practice to divide marine animals into the 

 three groups of Benthos, Nekton, and Plankton, according to 

 their locomotor possibilities. In the Benthos are included fixed 

 forms, and animals which creep upon the sea-floor, or burrow in 

 stone, sand, or mud. Adult corals^ for instance, possess no 

 power of moving from place to place, most crabs and sea-snails 

 live on the sea-floor, while many annelids and most bivalves 

 burrow. The Nekton is made up of animals, e.g. cetaceans 

 and fishes, which are powerful swimmers and easily range from 

 place to place of their own free-will. The Plankton fauna con- 

 sist of weaker creatures, and numerous larvae, which float or 



