ECOLOGY 23 



ing flagellates, the sun light is essential to photosynthesis (p. 107). The 

 sun light further plays an important role in those protozoans which 

 are dependent upon chromatophore-possessing organisms as chief 

 source of food supply. Hence the light is another factor concerned 

 with the distribution of free-living Protozoa. 



Chemical composition of water. The chemical nature of the water 

 is another important factor which influences the very existence of 

 Protozoa in a given body of water. Protozoa differ from one another 

 in morphological as well as physiological characteristics. Individual 

 protozoan species requires a certain chemical composition of the wa- 

 ter in which it can be cultivated under experimental conditions, al- 

 though this may be more or less variable among different forms 

 (Needham et al, 1937). 



In their "biological analysis of water" Kolkwitz and Marsson 

 (1908, 1909) distinguished four types of habitats for many aquatic 

 plant, and a few animal, organisms, which were based upon the kind 

 and amount of inorganic and organic matter and amount of oxygen 

 present in the water: namely, katharobic, oligosaprobic, mesosapro- 

 bic, and polysaprobic. Katharobic protozoans are those which live in 

 mountain springs, brooks, or ponds, the water of which is rich in 

 oxygen, but free from organic matter. Oligosaprobic forms are those 

 that inhabit waters which are rich in mineral matter, but in which 

 no purification processes are taking place. Many Phytomastigina, 

 various testaceans and many ciliates, such as Frontonia, Lacrymaria, 

 Oxytricha, Stylonychia, Vorticella, etc. inhabit such waters. Meso- 

 saprobic protozoans live in waters in which active oxidation and de- 

 composition of organic matter are taking place. The majority of 

 freshwater protozoans belong to this group: namely, numerous 

 Phytomastigina, Heliozoa, Zoomastigina, and all orders of Ciliata. 

 Finally polysaprobic forms are capable of living in waters which, 

 because of dominance of reduction and cleavage processes of organic 

 matter, contain at most a very small amount of oxygen and are rich 

 in carbonic acid gas and nitrogenous decomposition products. The 

 black bottom slime contains usually an abundance of ferrous sul- 

 phide and other sulphurous substances. Lauterborn (1901) called this 

 sapropelic. Examples of polysaprobic protozoans are Pelomyxa 

 palustris, Euglypha alveolata, Pamphagus armatus, Mastigamoeba, 

 Trepomonas agilis, Hexamita inflata, Rhynchomonas nasuta, Hetero- 

 nema acus, Bodo, Cercomonas, Dactylochlamys, Ctenostomata, etc. 

 The so-called "sewage organisms" abound in such habitat (Lackey, 

 1925). 



Certain free-living Protozoa which inhabit waters rich in decom- 



