Effects of Desiccation on the Rotifer 



239 



basis. The choice of 10 per cent, of course, was entirely arbitrary 

 but this number was found to be convenient and to give fairly 

 reliable results. In making the last determination it was neces- 

 sary to keep the animals for at least a day to be sure that no cases 

 of revival should be missed. For this reason, in this and all sim- 

 ilar experiments, the rotifers were dried in shallow glass dishes 

 which could be covered and thus the loss of the water added at the 

 end of the experiment prevented. A great fault to be found with 

 much of the previous work on the subject is that ordinary glass 

 slides were used with which on account of evaporation the rotifers 

 could not be kept under observation for more than a few hours. 

 Doubtless this is the reason why so many observers have been 

 unable to find evidences of revival after drying without sand. 



The results of the experiments, made with these precautions, 

 are given in the following table. It will be seen that the time 

 required for the first movements to appear is inversely proportional 

 to the percentage of recoveries; in other words, the slower the 

 movements are in appearing the greater is the mortality. This 

 relation was shown in a large number of experiments to be quite 

 general and knowing one quantity it is possible to predict in a 

 rough and approximate way the other. 



These experiments are in full accord with the view that the pro- 

 tective effect of the sand is due to the greater slowness of the dry- 

 ing process when it is present. If the mere presence of sand in 

 itself were sufficient to cause the rotifers to settle down and secrete 

 a capsule about themselves we should expect that a small quantity 

 would be almost as effective as a large quantity. This, however. 



