258 PLM'i-: or asm: Ron. is mijtabousm 



oil her tlic pi-esciicc or the absence of oxygen though gain- 

 iiig tlicir energy exclusively from anaerobic reactions. The 

 aerobic reactions which occur in the presence of oxy- 

 gen would not be related to the j)roduction of energy. 



(B) Amphibionts: animals capable of gaining energy 

 from l)oth aerobic and anaerobic processes. (1) Eiiroxy- 

 biotic oi-fjaiiisiHs: animals which normally gain their en- 

 ergy through aerobic metabolism, but whose anaerobic 

 functions are well enough developed to allow a long sur- 

 vival under anaerobic conditions. (2) Stenoxyhiotic or- 

 (/(uiisms: animals which normally gain their energy 

 through aerobic metabolism and wiiich do not survive long 

 under anaerobic conditions, either because anaerobic func- 

 tions are not well developed, or because the animals are 

 injured by the accumulating end products of the anaerobic 

 metabolism. 



Since this classification w^as published, new facts have 

 become knowni and a revision is necessary. The group 

 "anoxybiotic organisms," as defined above, is no longer 

 justified. The newer data on the metabolism of para- 

 sitic nematodes indicate clearly that these animals can 

 derive at least part of their energy from aerobic reac- 

 tions. Future investigations wall probably reveal similar 

 relationships in cestodes and trematodes. Another 

 change is necessitated by our increased knowledge con- 

 cerning the prevalence of energy-producing fermenta- 

 tions in the presence of air in many invertebrates. We, 

 therefore, propose the following revised classification. 



(A) Animals that gain their energy solely through an- 

 aerobic reactions; they are injured by relatively 

 low^ oxygen tensions. Example : sapropelic ciliates. 



(B) Animals capable of gaining energy from both 

 aerobic and anaerobic reactions. 



(1) Aero-fermenters: animals with a metabolism 

 characterized by the prevalence of incomplete 



