WATER EELATIONS OF OTHER SPECIES 



147 



eral, since the means (agents) used to attain these loads could be 

 considered as special and peculiar ones. 



This and the earthworm are the only invertebrate species for 

 which both turnovers and complete equilibration diagrams, includ- 

 ing total as well as net exchanges and loads of both signs, are avail- 

 able at present, so far as I know. Relative to body volume, turn- 

 over in Zoothamnium is a hundred times as rapid as in earthworm. 



<^ 53. Marine Zoothamnium 



In a marine species of the same genus, water output is measured 

 in diverse stationary states of water content (fig. 93). Loads are 



+50 +100 



Water Load 



Fig. 93. Steady rate of water output through contractile vacuoles (% of Bo/hour) 

 in relation to water load ( % of Bo) . Zoothamnium, peritrich ciliate, at 15° C. Each 

 point represents one test, of rate in diluted sea water, between two measurements of rate 

 in normal sea water. Data of Kitching ('34). 



secured by keeping individuals in any dilution of sea water for an 

 hour or more ; then body volumes and steady vacuolar outputs are 

 ascertained. Since the body volume remains constant, rate of water 

 intake equals rate of water output. 



Very often it is assumed that water continually leaks into such 

 an organism, whereupon the vacuoles pump it out, relieving the 

 body of fluid. The augmentation of rate, amounting to 20 times 

 the usual, and the shape of the curve in figure 93, suggest that the 

 rate of output is proportional to the reciprocal of the concentration 

 of the medium, a fact which allows the assumption of leakage. But 

 the effective concentration of the body substance in each state of 



