42 *"^r/?r/;)' or r\vi:irri:iHx'ATES 



they can live aiiacrobically for several weeks. It has 

 sometmies been assumed that significant amounts of 

 oxyg'en remained undetected in the above-mentioned 

 strata. But reliable investigators like Birge and Juday 

 are of the opinion that such is not the case. Further- 

 more, it is especially significant that at least one typi- 

 cally anaerobic ciliate has been found in this kind of habi- 

 tat. Juday (1919) encountered in Lake Mendota (Wis- 

 consin) a protozoon probably belonging to the genus 

 Enchclys which occurred only when the water appeared 

 free of oxygen (with the testing method he used). Later 

 Liebmann (1936a) identified Juday 's organism as En- 

 chelys vermicularis Smith, a typical anaerobic sewage 

 ciliate. 



B. RGlationship hetiveen availability of oxygen and its 

 utilisation. Among protozoa there probably occur all 

 gradations between the anaerobic forms mentioned above 

 and the organisms capable of leading normally only an 

 aerobic existence. Stromhidium may serve as an ex- 

 ample of the latter class. It disappears from cultures, 

 according to the findings of Galadziev and Malm (1929), 

 when the oxygen disappears. It is probably safe to as- 

 sume that all protozoa living in clear and well-aerated 

 water are, normally, aerobic, though they may exhibit a 

 certain tolerance for experimentally induced anaerobic 

 conditions. Some forms try to escape oxygen deficien- 

 cies by wandering away. Vorticella nehulifera forms a 

 posterior circle of cilia, separates from its stalk and 

 swims around with the help of the newly formed cilia, 

 until oxygen is restored to the medium. This mechan- 

 ism will enable such a normally sessile organism to search 

 in nature for a new place of attachment in surround- 

 ings having sufficient oxygen. 



Loxodes rostrum seems to be a typical intermediate 

 form. The oxygen relationships of this ciliate in its nat- 

 ural habitat were studied by Rylov (1923). He encoun- 

 tered most of the specimens in water strata containing 



