114 SUIiVEY OF INVERTEBRATES 



lack of oxygen accumulate within their bodies endprod- 

 ucts of incomplete oxidations or fermentations, which 

 sooner or later will prove toxic unless removed. The re- 

 moval, however, can be accomplished in this group of ani- 

 mals only by aerobic processes that take place when oxy- 

 gen is again available, and apparently not by excretion. 

 These products accordingly occasion an excess oxygen 

 consumption, the repayment of the incurred oxygen debt. 

 Studying then the post-anaerobic oxygen consumption of 

 Chirononius tJiummi and Eut any tarsus inermipes, Har- 

 nisch found that in both species characteristic curves 

 were obtained if the preceding anaerobic period had not 

 been too long. If it was too long, the repair mechanism 

 was damaged and the animals did not fully recover. But 

 a significant point is that the recovery mechanism failed 

 earlier in Entanytarsus than in Chironomus, i.e., in the 

 species that normally does not invade habitats poor in 

 oxygen. Harnisch's tentative conclusion is that the po- 

 tency of the recovery mechanism might be more decisive 

 than anything else in determining to what extent oxygen 

 may be the limiting factor in the distribution of the 

 midge larvae. 



In a still later publication the same author (1939) de- 

 scribes yet another mechanism which he studied, so far, 

 only in Chironomus thummi. He observed that during 

 short periods of anaerobiosis lower fatty acids accumu- 

 late in the body in greater amounts than during long- 

 lasting periods. Harnisch believes that some of these 

 acids are removed little by little through oxidations, de- 

 spite the lack of oxygen in the immediate surroundings. 

 The oxygen necessary would originate from the trans- 

 formation of glycogen into fat, a process occurring in the 

 later stages of anaerobiosis. It is obvious that the sig- 

 nificance of this mechanism for the ecological distribu- 

 tion can be estimated correctly only after further inves- 

 tigation will have shown whether or not its potency is 

 markedly different in various species. One wonders 



