286 SUMMARY 



the oxidjilioii-rcdiiclion i)()l('iitial of the medium in much 

 the same way as do bacteria. In nature, inorganic con- 

 stituents and the bacterial llora will be more important 

 than the metabolism of the animals themselves in de- 

 termining the oxidation-reduction potentials of a given 

 habitat. Endamoeba and Opisthorchis, two organisms 

 living in nature in surroundings poor in oxygen, survive 

 best, ill vitro, in media having low potentials. 



5, The data on the adjustability of the internal oxida- 

 tion-reduction potential to the oxygen content of the sur- 

 roundings in purely aerobic animals and in invertebrates 

 with well-developed anaerobic functions fail as yet to 

 demonstrate a distinctive difference between the two 

 groups. 



TJw origin of anaerohiosis in invcrfcbrates. 



1. Several arguments (phylogenetic considerations, 

 theory of recapitulation, geophysical theories concerning 

 the origin of the atmospheric oxygen), which have been 

 put forward in support of the idea of the phylogenetic pre- 

 cedence of anaerohiosis, are not well grounded. The 

 only argument which has some weight is the ubiquity of 

 reducing processes and the fact that anaerobic reactions 

 occur first in the chain of energy-producing metabolic 

 processes. 



Anaerohiosis and the origin of endoparasitism. 



1. The idea that intestinal worms and insect larvae 

 are derived from anaerobic mud-dwelling ancestors 

 seems, on the whole, not well-founded, although the 

 theory may perhaps still be held for intestinal nematodes. 



2. The theory that the wanderings of many parasitic 

 nematode larvae within the body of vertebrate hosts, be- 

 fore the parasites settle down in the intestine, are corre- 

 lated with the necessity of leading, in the latter habitat, 

 an anaerobic life, is not supported by experimental evi- 

 dence. 



3. A derivation of the present-day sapropelic-, rumen- 

 and termite-protozoa from the same mud-dwelling ances- 

 tors appears possible from a physiological standpoint. 



