104 SURVEY OF INVERTEBRATES 



ever, is that the decline of the oxygen consumption goes 

 farther than can be explained merely by lowered energy- 

 needs due to cessation of all muscular movements. When 

 such animals are brought back into water of normal sa- 

 linity, their oxygen consumption is markedly higher 

 than normal. In other words, they have contracted an 

 oxygen debt — an indication that partially oxidized sub- 

 stances have accumulated in their bodies. 



Decapod crustaceans, such as crabs or crayfish, show 

 little resistance in experimentally induced anaerobic con- 

 ditions (Table 13). It is true that crayfish are sometimes 

 found in highly polluted waters where only traces of 

 oxygen are present (Jewell, 1918) but they probably do 

 not stay long in such environment. It should further 

 be remembered that crayfish are able to regulate their 

 respiratory movements (c/. Peters, 1938; Jordan and 

 Guittart, 1938) which become proportionately more fre- 

 quent as the oxygen supply of the water becomes poorer. 

 It is possible, however, that at very low tensions this 

 mechanism becomes inadequate and that the animal is 

 then forced to resort to incomplete oxidations. 



It should be realized, in this connection, that the oxy- 

 gen consumption of most decapods is independent of the 

 tension over a wide range (some exceptions are known). 

 Data concerning this point are presented by Henze 

 (1910), Amber son, Mayerson and Scott (1924), Helff 

 (1928), Hiestand (1931), and Maloeuf (1937). Hiestaud 

 has collected some evidence indicating that an oxygen 

 debt may be built up in crayfish, and Maloeuf (1936) has 

 demonstrated that the respiratory quotient of these ani- 

 mals rises at low tensions. 



A few other isolated observations concerning the influ- 

 ence of a lack of oxygen on crustaceans may finally be 

 mentioned here. Frohlich (1938) reports that asphyx- 

 iation of Daphnia pulex proceeds more slowly in the wa- 

 ter of the hot springs of Gastein than in ordinary water 



