60 SURVEY or l\ VERTEBRATES 



II. COELENTERATES 



In nature, coelenterates do not seem to occur in anoxic 

 habitats. They exhibit, nevertheless, a certain tolerance 

 for experimental deprivation of oxygen. 



It has been shown that hydras may survive several 

 hours in anaerobic conditions (Welch and Loomis, 1924; 

 Beutler, 1933). Normally, however, these animals lead 

 an aerobic life and even prefer water rich in oxygen. 

 After several days in water of very low oxygen con- 

 tent they are irreparably damaged. 



Beutler (1933) has demonstrated, furthermore, that 

 brown species of Hydra are actually attracted by oxygen, 

 i.e., they exhibit an oxygeno-taxis. In green species this 

 phenomenon takes place also but only in the dark, appa- 

 rently because, in the light, the symbiotic algae are able 

 to provide sufficient oxygen to render such a reaction 

 unnecessary. 



Whether or not actinians can be kept for any length of 

 time under strictly anaerobic conditions is as yet un- 

 known. There is no reason to assume that in nature 

 they are apt to support long-lasting anoxic conditions. 

 We do know, however, that they are able to survive in 

 water containing but little oxygen. Their behavior un- 

 der such conditions has led to a controversy between Pie- 

 ron (1908, 1908a,b,c,d) and Bohn (1908, 1908a). The 

 former maintains that the animals contract in water poor 

 in oxygen, while the latter asserts that they expand. 

 The problem is still unsolved and should be reinvesti- 

 gated. The actinians have been recognized long ago 

 (Henze, 1910) as being among the best examples of ani- 

 mals whose oxygen consumption depends on the oxygen 

 tension. On the other hand, their oxygen consumption is 

 far below maximal even when the water is saturated with 

 air. It appears probable therefore that the deeper lying 

 tissues depend at least in part on anaerobic processes for 

 the supply of energy required by the cells. This problem 

 will be discussed later. 



