104 Aquatic Organisms 



concentration of sewage, and decrease of current. The 

 water of the stream was of a Hvid greenish yellow tinge. 

 * * * The distribution of Carteria in the river was 

 remarkable. It formed great bands or streaks visible 

 near the surface, or masses which in form simulated 

 cloud effects. The distribution was plainly uneven, 

 giving a banded or mottled appearance to the stream. 

 The bands, lo to 15 meters in width, ran with the 

 channel or current, and their position and form were 

 plainly influenced by these factors. No cause was 

 apparent for the mottled regions. This phenomenon 

 stands in somewhat sharp contrast with the usual 

 distribution of waterbloom upon the river, which is 

 generally composed largely of Euglena. This presents 

 a much more uniform distribution, and unlike Carteria, 

 is plainly visible only when it is accumiolated as a super- 

 ficial scum or film. Carteria was present in such quan- 

 tity that its distribution was evident at lower levels so 

 far as the turbidity would permit it to be seen. It 

 aft'orded a striking instance of marked inequalities in 

 distribution." 



Similar green flagellates of wide distribution are 

 Chlamydomonas and Sphaerella (fig. 306) commonly 

 found in rainwater pools. 



Certain aggregates of such cells into colonies are very 

 beautiful and interesting. Small groups of such green 

 cells are held together in flat clusters in Gonimn and 

 Platydorina, or in a hollow sphere, with radiating 

 flagella that beat harmoniously to produce a regular 

 rolling locomotion in Pandorina (fig. 30 e), Eudorina 

 and Vol vox. 



Volvox — The largest and best integrated of these 

 spherical colonies is Volvox (fig. 31). Each colony may 

 consist of many thousands of cells, forming a sphere 

 that is readily visible to the unaided eye. It rotates 



