THE BIOSPHERE 1007 



BIONOlAHC CHARACTERISTICS OF ANIMALS.* 

 I. Protozoa. 



FoRAMiNiFERA. The Foraminifera are typically marine organ- 

 isms, though a considerable number of species has become adapted 

 to brackish water, living in estuaries and near the mouths of 

 streams, while many species, commonly placed in this class, live 

 entirely in fresh water. Their distribution is so great that scarcely 

 any marine sediments are wholly free from the shells of these ani- 

 mals. Most Foraminifera belong to the 'vagrant benthos, though 

 sedentary benthonic forms also occur. Only something over twenty 

 living planktonic species are known, these belonging chiefly to the 

 genera Globigerina, Orbulina. and Pulvinulina (Figs. 101-103), the 

 first predominating. The small number of species is, however, 

 counterbalanced by the enormous number of individuals. The ben- 

 thonic Foraminifera are confined chiefly to the littoral district, where 

 the character of the bottom and the temperature of the water exert 

 important influences on the distribution of these organisms. A 

 muddy facies of the sea-bottom seems to be conducive to the ex- 

 istence of a large number of species, but the rocky bottoms are not 

 without their types ; while algae and sea-grasses commonly form the 

 home of vast numbers of these organisms. The coarse, sandy and 

 gravelly bottoms are not generally inhabited by these animals, 

 though their dead shells are not uncommon in the sands along our 

 beaches ; while along some shores, they are so abundant as to con- 

 stitute the greater portion, if not the whole, of the deposit. Dana (9) 

 states that in the Great Barrier-reef region of Australia the shells 

 of Orbitolites are so abundant that . . . "they seemed in some 

 places to make up the whole sand of the beaches, both of the 

 coral islets and of the neighboring Australian shore." 



The vertical range of the benthonic Foraminifera is very great, 

 species sometimes passing through a range of several thousand 

 fathoms. In such cases there is often a change in the size or 

 thickness of the shell with the change in depth. Although the 

 planktonic Foraminifera comprise so few species, the number of 

 their individuals is enormous. From their shells the Globigerina 

 oozes form in deep water, where no sediment is carried ; but it is 

 evident that, in a region where the land is reduced to near base- 

 level, so that little or no sediment is carried into the sea, pure 

 accumulations of such shells will occur near shore, thus, forming a 



* Only those represented by fossils are taken into account here. 



