SURVEY OF IXVEFTEBRATES 69 



body. The latter are quite generally toxic and the level 

 they reach is probably often the factor limiting the anaer- 

 obic resistance. 



The most extreme cases of reduced metabolism are 

 those of completely dried organisms. In them, life proc- 

 esses are obviously reduced to a minimum, if indeed 

 they do not cease completely. That animals in a state 

 of suspended animation should be more resistant to the 

 lack of oxygen than in the active stages is so obvious, 

 that it needs no further comment. Experiments prov- 

 ing this have been performed by Eahm (1929) with moss- 

 inhabiting nematodes and rotatoria and by Becquerel 

 (1936) with three species of rotatoria. 



The nutritional stage is another factor often involved 

 in determining the energy requirements. It is of interest, 

 in this connection, that engorged specimens of Eirudo 

 medicinalis die more rapidly under anoxic conditions than 

 leeches which have been starved for several months (Flit- 

 ter, 1908). On the other hand, it is a well-established 

 fact that leeches starving under aerobic conditions have 

 lower energy requirements than fed ones. This is evi- 

 denced by their smaller oxygen consumption. It seems 

 logical to assume that an identical situation prevails un- 

 der anaerobic conditions and that the relatively low rate 

 of anaerobic metabolism explains the increased resis- 

 tance in anoxic conditions observed in unfed specimens. 



Not all worms, however, have a lowered rate of me- 

 tabolism during starvation. According to Hyman (1919), 

 after a high oxygen consumption which is due to the 

 presence of food and which lasts only a few hours in 

 planarians, the rate decreases, reaching a minimum with- 

 in the first two weeks of starvation and, after that time, 

 a marked and progressive increase is observed. Starving 

 planarians should, if the above assumption of an in- 

 verse correlation between rate of metabolism and resis- 

 tance in anaerobic medium is correct, be more affected by 

 lack of oxygen than specimens which had been fed prior 



