70 STUDIES IN ANIMAL LIFE. 



for certainly in my experience a much more mod- - 

 erate desiccation — ^namely, that obtained by simple 

 evaporation over a mantelpiece or under a large 

 bell-glass — always destroyed the animals if httle or 

 no dirt were present. 



The subject has recently been brought before the 

 French Academy of Sciences by M. Davaine, whose 

 experiments* lead him to the conclusion that those 

 Eotifers which habitually live in ponds will not re- 

 vive after desiccation, whereas those which live in 

 moss always do so. I believe the explanation to be 

 this : the Eotifers living in ponds are dried without 

 any protecting dirt or moss, and that is the reasc^ 

 they do not revive. 



After having satisfied myself on this point, I did 

 what perhaps would have saved me some trouble 

 if thought of before. I took down Spallanzani, and 

 read his account of his celebrated experiments. To 

 my surprise and satisfaction, it appeared that he 

 had accurately observed the same facts, but curious- 

 ly missed their real significance. Nothing can be 

 plainer than the following passage : " But there is 

 ohe condition indispensable to the resurrection of 

 wheel-animals : it is absolutely necessary that there 

 should be a certain quantity of sand; without it 

 they will not revive. One day I had two wheel- 

 animals traversing a drop of water about to evapo- 

 rate which contained very little sand. Three quar- 

 ters of an hour after evaporation they were dry and 

 * Davaine in AnnaUs des Sciences Nalurelles, 1858, x., p. 335. 



