26 BIOLOGY OF THE PROTOZOA 



Europe, Asia, Siberia, Africa, South America and Australia; they 

 are cosmopohtan, and the temptation to describe new species because 

 they happen to have been found in some hitherto unexplored local- 

 ity has no justification from the facts of geographical distribution. 

 This is particularly applicable to the fresh water forms but does not 

 apply equally to the deep sea t\'pes. The littoral fauna of salt 

 water like the fresh water forms, appear to have a cosmopolitan 

 distribution according to the observations of Gourret and Roesser 

 (1886), of Levander and of Hamburger and Buddenbrock in Europe, 

 and in North America where the brackish waters are particularly 

 rich in number and variety of Protozoa. The pelagic and deep 

 sea forms appear to be unequally distributed; some types are 

 apparently limited to the Indian Ocean; others to the Atlantic, 

 while many tropical genera and species, especially of Radiolaria 

 and Foraminifera, are not found in the polar seas and vice versa. 

 Some strictly pelagic forms on the other hand, notably Noctiluca 

 jiiiliaris, are found on or near the surface of sea water in all parts 

 of the world. 



Observations are sufficiently numerous to show that not only is 

 there a certain climatic distribution of salt water forms, but a 

 vertical distribution as well. Certain genera and species of Radio- 

 laria and Foraminifera are present in the surface waters but are 

 never found at the depth of from 600 to 3000 feet, while some fam- 

 ilies, notably the Challengeridse and Tuscaroidee, are present only 

 in the extreme depths of the sea. 



Many species are sufficiently adaptable to live either in fresh, 

 brackish or salt water; indeed most of the common forms of rhizo- 

 pods, flagellates and ciliates seem to be equally at home in either. 

 Many types, however, sometimes entire groups of Protozoa, are 

 not so ubiquitous; the sub-class Radiolaria for example, comprising 

 more species than any other entire class of Protozoa, are exclusively 

 marine, while another large sub-class of the Sarcodina, the Fora- 

 minifera, comprises only a few fresh water representative species. 

 Many more types of Dinofiagellata are present in salt than in fresh 

 water. Ciliates are poorly represented in the deep sea, although 

 one famil}'— Tintinnidae— is wonderfully rich in salt water forms 

 while fresh water forms are uncommon. Heliozoa, another sub- 

 class of the Sarcodina, on the other hand, are typically fresh water 

 forms with relati^'ely few salt water representatives. Many forms, 

 especially the chlorophyll-bearing flagellates, are too sensitive to 

 live vigorously in stagnant waters but thrive in the pure water of 

 lakes and reservoirs, a predilection on their part which frequently 

 leads to offensive odors and tastes in natural drinking waters 

 (Uroglenoysis amcricona, Symira uxella). 



The distribution of parasitic forms belonging to all groups of the 

 Protozoa, obviously follows the distribution of their hosts and we 



