Effects of Desiccation on the Rotifer 23 1 



contact with the sand is due entirely to the fact that as the water 

 disappears their movements become more and more restricted 

 until they finally come to an end in its vicinity where the water 

 lingers longest. It is true that the presence of sand is beneficial 

 in the drying process but, as experiments to be mentioned later 

 show, this is due entirely to the greater slowness of the drying under 

 these circumstances and not to any preparations the animal makes 

 to resist desiccation. That the presence of sand is responsible for 

 no essential difference in behavior is shown by the fact that roti- 

 fers dried with a small quantity of sand show practically as great 

 a mortality as those dried with none at all. If the mere presence 

 of the sand enabled the rotifers to encyst themselves normally, we 

 should not expect this to be so. If, on the other hand, the effect 

 is merely one of the rapidity of evaporation, the fact finds a ready 

 explanation. 



It is seen, therefore, that the two points of originahty in Davis' 

 view, namely, the presence of protective secretion and a difference 

 in the behavior of the rotifers when dried under different conditions 

 are both based upon too shght evidence and are not confirmed 

 by more careful observations. So far as his arguments go, there 

 is no reason to believe that rotifers exposed to conditions of dry- 

 ness can escape a true desiccation. On the other hand, in addi- 

 tion to this negative evidence there is much positive evidence in 

 favor of the view that an actual drying does occur. 



2 Evidence for the View that True Desiccation Occurs 



In the first place, it must be noted that during the process of 

 desiccation there are very marked changes in the size and form 

 of the rotifers. Shrinkage always occurs and there may be con- 

 siderable distortion of the body if the drying is rapid enough. 

 According to Davis' view we should expect such shrinkage only in 

 rotifers dried on a clean slide which are killed by the process. The 

 fact is, however, that it occurs in all cases. When rotifers are 

 very slowly dried, with or without sand, they retain their original 

 form very perfectly and fairly accurate estimates may be made 

 of their loss in volume during the drying process. From careful 



