GEOGRAPHICAL DISTRIBUTION. 11/ 



zones of coast vegetation are recognized in the tropics by 

 Schimper: the Pescapnii formation, the Barringtonia forma- 

 tion, the Xipa formation, and the Mangrove formation. 



The fauna of the coast is also determined in its composi- 

 tion by the conditions of the shore itself, and thus we find 

 different kinds of animals associated with the rock beach, the 

 bowlder beach, the pebble beach, the sand beach, and the 

 mud beach. 



Under the sea surface downward a number of zones have 

 been distinguished, defined most easily by their depth, \\hich 

 present strong contrast in their faunas. We owe it to Ed- 

 M'ard Forbes that we have a nomenclature for these zones of 

 depth. The di\-isions made by him are the littoral zone, the 

 laminarian, coralline, and the deep-sea zones ; the latter, as the 

 result of deep-sea dredgings. has been divided into the zone 

 of deep-sea corals, or brachiopod zone, and the abyssal zone. 



In a Report of investigations made upon the faunas of the 

 seas off the New England coast. Professors Verrill and Smith 

 found it to be a fact " that there are in the waters of this re- 

 gion three quite distinct assemblages of animal life, which are 

 dependent upon and limited by definite physical conditions 

 of the waters which they inhabit."" These are described 

 under the follo^^■ing divisions, viz. : 



1. The fauna of bays and sounds; 



2. The fauna of the estuaries and other brackish waters; 



3. The fauna of the cold waters of the ocean shores and 

 outer banks and channels. 



This classification of environments is not bathymetric, but 

 is chiefly on the basis of temperature and purity of the waters. 



It is altogether probable that every kind of difference in 

 the environment, which could be described as beneficial or 

 otherwise to the vital functions of organisms, is also repre- 

 sented by greater or less adaptation of the organization, to 

 profit by the favorable conditions or to avoid the evil effects 

 of those which are unfavorable. 



Relations of Organisms to Time and to Environment Equally 

 Significant. — When we consider alone the historical relations 



* United States Fish Commission, "Report upon the Invertebrate Animals 

 of Vineyard Sound and Adjacent Waters," p. 5, etc. 



