PELAGIC ANIMAL LIFE 563 



occurrence of certain species is subject to great variation in 

 different regions. We shall, therefore, dispense with the many 

 Latin and Greek terms employed to define such groups of 

 pelagic organisms, and simply use the term " bathypelagic " 

 to denote those animals that live deep in the intermediate 

 layers. Hensen proposed the term " plankton " to denote 

 every kind of organism floating or drifting in the water, either 

 shallow or deep, "dead or living," and Haeckel applied it so 

 as to include all pelagic animal and plant life as a whole, in 

 contrast to bottom-life as a whole, which he terms " benthos." 



In this chapter I propose to consider only the different 

 species or communities of pelagic animals, not the pelagic life 

 as a whole. Pelagic forms occur in all classes of the animal 

 kingdom from the unicellular Protozoa to the fishes ; to mention 

 them all would be to write a text-book on zoology. The chief 

 aim of this book is however to give some of the general and 

 special results of the cruises of the " Michael Sars," A discussion 

 of the results relating to pelagic animals (as with the bottom- 

 fish) calls for some information about the principal forms, so I 

 commence with a short review of pelagic animals.^ In the 

 absence of descriptions of the animals, the illustrations will give 

 the reader an idea of some of the forms referred to. Their 

 geographical distribution, as known from previous expeditions, 

 is briefly indicated, and in a later section I shall deal with the 

 distribution of the most important animals in their communities 

 in the different areas of the North Atlantic and the Norwegian 

 Sea. 



I. Short Review of Pelagic Animals 



Among unicellular animals the Foraminifera and the Radiolaria may- 

 be given prominence. Being exceedingly rich in species, as well as 

 individuals, they play an enormous part in the economy of the ocean, 

 and their shells constitute an essential portion of the deposits on the 

 ocean-floor. 



The pelagic foraminifera have shells of carbonate of lime, usually Foraminifera. 

 divided into several chambers communicating with each other, allowing 

 the protoplasm to penetrate the whole shell, which is perforated by 

 innumerable small apertures (foramina), through which the finest threads 

 of the protoplasm (the pseudopodia) may pass. In Chapter IV. 

 p. 172, a list is given of all the species known to be pelagic, and certain 

 important forms are figured. The list embraces eight genera and 

 twenty-six species, fourteen of which belong to the genus Globigerina, 

 also represented by an enormous number of individuals. During the 



^ A very useful review of the results of modern (especially German) investigations is given in 

 Steuer's PlanMonkiinde (Leipzig and Berlin, 1910), with extensive lists of literature. 



