144 



TRANSITION TO ANAEROBTOSTS 



TABLE 19 



Relative Oxygen Consumption of Whole Sections Thkough the Body 

 Wall of Actinians, and of Minced Pieces. 



Mean values calculated from the data presented by Harnisch, 1932. 



But the following observation by Petrik (1931) raises 

 another difficulty. He found that the oxygen consump- 

 tion of fed actinians is considerably higher than that 

 of starving ones, and that it stays higher for several 

 days. Since the oxygen consumption of unfed speci- 

 mens is supposed to be already at its maximum, being lim- 

 ited only by diffusion, the increased rate can only be un- 

 derstood if, by a regulatory mechanism, feeding increases 

 the surface through which oxygen can enter the body. 

 There seems indeed to be such a regulatory mechanism: 

 fed actinians- swell up, due to water intake, and in this 

 way increase their body surface to a noticeable degree 

 (the ratio of the surface of absorption to the amount of 

 organic material thus becoming higher). 



A situation similar to that prevailing in actinians prob- 

 ably exists also in other bulky animals lacking a circula- 

 tory system, like the large worm, Sipunculus, and per- 

 haps also in sea-urchins, starfish and other organisms 

 that possess neither a true circulatory system nor a 

 powerful respiratory pigment. Furthermore, a sea-ur- 



