SURVEY OF INVERTEBRATES 



41 



ter. He introduced sewage material containing both spe- 

 cies into tall cylinders; one cylinder was then aerated 

 by means of compressed air forced through porous plates 

 at the base, while the other remained unaerated. The re- 

 sults of these experiments are shown in Table 8. A 

 striking ditference between the two forms is evident. 

 Trepomonas disappeared only in the aerated culture and 

 Opercularia only in the non-aerated one. Lackey is 

 probably correct in assuming that in these experiments 

 the presence or absence of oxygen was the deciding fac- 

 tor, for it is known that other factors, such as variations 

 in pH, temperature, food, and gases other than oxygen, 

 do not have much influence on the organisms experi- 

 mented upon. 



TABLE 8 



Active Trepomonas and Opercularia in Aerated and Non-aerated 

 Sewage (According to Lackey, 1932). 



Another anaerobic habitat for non-parasitic protozoa 

 is represented by the stagnating strata of fresh water 

 lakes (Juday, 1908; Birge and Juday, 1911; Imel, 1915; 

 Moore, 1939; Zhinkin, 1930). Most, but not all protozoa 

 reported from this habitat {cf. Appendix, Table 3) are 

 regularly found also in well-aerated surroundings. It 

 seems, therefore, obvious that they live aerobically when 

 oxygen is present, and that, in the absence of oxygen, 



