356 BIOLOGY OF THE PROTOZOA 



Rhizopods and ciliates are represented by fewer genera and 

 species than are flagellates. Of the 250 species of Protozoa living 

 in the soil Sandon enumerates only 48 species of rhizopods and 35 

 species of ciliates; nor are they so widely distributed among the 

 146 soils from all parts of the world. Limax amebae were regis- 

 tered from 49.5 per cent of all sample soils examined ; HartmanneUa 

 hyalina, from 42 per cent; Nuclearia, from 27 per cent; Trinema 

 enchelys, from 22 per cent; Trinema lineare, 19 per cent; and Nagleria 

 gruberi, from 17.5 per cent. Of ciliates, Colpoda cucculus, Colpoda 

 steinii and Cyclidium glaucoma were present in 56, 47 and 23 per 

 cent respectively. 



Few generalizations, however, can be made regarding soil-dwel- 

 ling forms as distinct from other Protozoa, and there is but little 

 evidence that morphological adaptations follow such a mode of 

 life. This phase of Protozoology, however, is still young and 

 further study will undoubtedly lead to important deductions as 

 well as to practical results. 



4. The Sapropelic Flagellates.— Under the term "sapropelic 

 fauna" Lauterborn (1901) included Protozoa which are able to 

 live in media partly or wholly free from oxygen. Some of the soil 

 flagellates, particularly those living deep in the soil, are partially 

 anaerobic, and might well be included here. The majority of sapro- 

 pelic flagellates, however, live in sulphurous waters and in sewage, 

 especially in the deeper zones of sewage filtration tanks where 

 oxygen is entirely absent (polysaprobic forms, Kolkwitz, 1908). 



The sapropelic fauna, according to Lauterborn, includes those 

 forms which live and multiply in the slime on the bottom of fresh 

 ponds or salt water pools and ditches. This slime consists, for the 

 most part, of plant debris and animal excrement and remains, while 

 inorganic mineral matters are reduced to a minimum. Necessary 

 conditions leading to the accumulation of the necessary ingredients 

 for building up this environment are: (1) A rich growth of vegeta- 

 tion in the surface water; (2) standing water free from currents; 

 (3) protection against intense sunlight. In still waters dead plants 

 and animals from the surface settle on the bottom where the protein 

 materials decompose rapidly, giving rise to foul-smelling gaseous 

 products such as sulphuretted hydrogen, marsh gas, carbonic acid 

 and the like. If direct sunlight is present there is an active pro- 

 duction of oxygen by green plants, and with the aid of aerobic 

 bacteria progressive oxidation causes the splitting up of organic 

 matters until stabile inorganic combinations result. Under such 

 conditions a slime suitable for sapropelic forms does not accumulate, 

 hence for a proper medium oxygen must be absent. 



With the proper anaerobic conditions a fairly characteristic 

 sapropelic fauna develops. Many types are intermediate and may 

 live as semi-anaerobic forms, but others are obligatory anaerobes 



