DIFFERENCES I\ AXAEh'OB. F( XCT/OXS 263 



gaiiK'd by anaerobically kept invertebrates are those 

 made on Ascaris by Meier (1931). He found a heat pro- 

 duction of O.oOO g. eal. per gram per hour, but a com- 

 parison with worms kept under aerobic conditions is not 

 possible since no data for tlie latter are available; fur- 

 thermore Ascaris is an organism which under natural 

 conditions leads a predominantly anaerobic life. There is 

 a good deal of indirect evidence, however, that many nor- 

 mally aerobic invertebrates can gain all the energy needed 

 for the maintenance of thei'r normal life processes even 

 during protracted periods of oxygen deficiency. This can 

 reasonably be assumed in all those previously reviewed 

 cases in which the organisms survive for a long time 

 without visible damage. In many free-living or parasitic 

 protozoa and worms the anaerobic energy production 

 must be relatively high since the animals are able to 

 move freely in the absence of oxygen. In other in- 

 stances, as in TrichineUa larvae and in most clams, the 

 energy requirements are doubtless lowered since the mus- 

 cular movements cease; but the anaerobic processes are 

 still potent enough to maintain the animals alive. A last 

 group which includes the majority of the hitherto studied 

 insects, consists of animals that are incapable of gaining 

 much energy under anaerobic conditions, as evidenced by 

 their short survival time. It is not possible at present 

 to decide whether their biochemical organization, per- 

 haps their cellular enzyme complex, does not allow fer- 

 mentations, or whether some organ or tissue is rapidly in- 

 jured by the accumulation of end products of the anaero- 

 bic metabolism. 



One may approach this problem experimentally by 

 studying more thoroughly the resistance of the various 

 tissues of a given animal against asphyxiation and, at 

 the same time, determining the rate of anaerobic me'tab- 

 olism. Such a study might reveal that the inability of 

 the nervous system to withstand the deprivation of oxy- 



