PART III 



GENERAL ADAPTATION TO THE LACK OF 

 OXYGEN AND ORIGIN OF ANAEROBIOSIS 



CHAPTER I 



THE PLACE OF ANAEROBIC PROCESSES IN THE 

 GENERAL METABOLISM OF INVERTEBRATES 



Our survey of the reactions of invertebrates to the 

 lack of oxygen showed that there are various degrees of 

 resistance to asphyxiation. Some organisms, like the 

 sapropelic ciliates and a number of sewage protozoa, 

 seem to be obligate anaerobes, i.e., they thrive only if 

 oxygen is practically absent. Others are facultative an- 

 aerobes, i.e., they normally live in surroundings rich in 

 oxygen, but can withstand the absence of that gas for a 

 certain length of time. The majority of invertebrates 

 reviewed (but not necessarily the majority of all inver- 

 tebrates) fall into this category. A last group can be 

 termed obligate aerobes. These show only a negligible 

 resistance to the lack of oxygen; such are the cephalo- 

 pods. 



While this classification is quite conveni(^nt for the dis- 

 cussion of ecological relationships, it is clearly insuffi- 

 cient to characterize the various modes of energy pro- 

 duction and to bring out the relative importance of an- 

 aerobic processes in the life and metabolism of various 

 animals. Von Brand and Harnisch (1938) proposed the 

 follomng classification which is based on the mode of 

 energy production. 



(A) MoNOBiONTs: animals gaining their energy exclu- 

 sively through anaerobic reactions. ( 1) Anaerobic organ- 

 isms: animals injured even by low oxygen tensions. (2) 

 Anoxybiotic organisms: animals capable of living in 



