238 RE('0\ 1:RY from ANAJ'JROniOHfH 



general seem incapable of excreting the end products of 

 their anaerobic nietal)()lism. A study of the chemical 

 processes during recovery will be necessary before the 

 significance of Gilmour's figure can be understood. 



In a second group of invertebrates the oxygen debt is 

 repaid in full. The first case to be mentioned is that of 

 Planorbis corneus, investigated by Borden (1931). The 

 calculation of the excess oxygen consumption of this or- 

 ganism is more complicated than in many other in- 

 stances, because this snail contains relatively large 

 amounts of haemoglobin. The actual period of anaero- 

 biosis will therefore be shorter than the time during 

 which the animals are kept in the absence of oxygen, since 

 a certain amount of oxygen is stored in their blood. On 

 the other hand, that oxygen which is required, during 

 the post-anaerobic period, to transform the reduced 

 haemoglobin into oxy-haemoglobin must be subtracted 

 from the excess oxygen actually consumed, since obvious- 

 ly only the oxygen used in the cellular metabolism can 

 be considered as true excess oxygen. Borden took these 

 points into careful consideration ; her findings are illus- 

 trated in Figure 7. 



The situation is less complicated in animals which pos- 

 sess no respiratory pigment or which have only a small 

 amount of blood. Davis and Slater found a total re- 

 payment of the oxygen debt in cock-roaches (1926a, cf. 

 Fig. 8) and an almost total one in the earthworm (1928a). 

 Curiously enough. Lesser (1910a) had previously de- 

 scribed a diminished rate of oxygen consumption during 

 the recovery period of this latter organism. Perhaps his 

 animals had been damaged during the preceding anaero- 

 bic period. Bodine (1928) also reported an approximate 

 total repayment of the oxygen debt in grasshoppers. 



In a last group of invertebrates more oxygen is con- 

 sumed than is necessary to make up for the deficit in- 

 curred during anaerobiosis. Thus in Cryptoccrcus punc- 



