274 ORIGIN OF ANAEROBIOSIS 



lum can a connection between the ability to liveanaerob- 

 ically and the morphological organization -be estab- 

 lished. Even looking upon the animal kingdom as a 

 whole one fails to perceive the postulated phylogenetic 

 relationship. The anaerobic functions found in different 

 groups are most frequently related to ecological factors. 

 One would, furthermore, not be justified in speculating 

 whether a certain animal became established in an an- 

 aerobic habitat because it had inherited from its an- 

 cestors well-developed anaerobic functions, or whether 

 the latter became more pronounced during adaptation to 

 environments with progressively depleted oxygen supply 

 (for exceptions to this statement, cf. below. Chapter 4). 



To point 4 : Snyder believes that the theory of recapit- 

 ulation offers support to his idea of anaerobiosis as the 

 primitive condition. He mentions some organisms in 

 which the developmental stages are more resistant than 

 the adults when deprived of oxygen. Koschtojanz (1935a) 

 has recently again emphasized this point. Such cases un- 

 doubtedly do occur; the reproductive cells of echino- 

 derms, for example, are more resistant than the adults. 

 But this behavior is by no means universal. Thus the 

 juvenile stages of many trematodes seem to require more 

 oxygen than the fully developed worms. (It may be add- 

 ed that the recapitulation theory itself has lost some of 

 the prestige that it enjoyed thirty years ago.) 



Much more weight must be given to the arguments 

 contained in Snyder's point 2, point 3 (in part) and, per- 

 haps, also point 5. 



To point 2 and point 3 (in part) : Snyder emphasizes 

 that the function of oxygen is largely that of a waste 

 remover, or, in the expressive words of Clark (1924) 

 that of ''a scavenger cleaning up the waste products of 

 metabolism by combustion." It is indeed generally ac- 

 knowledged that the initial steps of practically all the 

 energy-producing processes within the animal body re- 



