Effects of Desiccation on the Rotifer 233 



body — perhaps even in a special secretion surrounding it. The 

 following experiment shows clearly that this was not the case. A 

 number of rotifers were stained intra vitam with neutral red and 

 then carefully dried. Several were tested to be sure that revival 

 occurred normally on the addition of water. Others were then 

 subjected in the dish in which they were dried, to moist ammonia 

 fumes, being kept under observation all the while. Almost imme- 

 diately the internal organs, which had stained deeply in the neutral 

 red, began to change color and in less than a minute had become 

 yellow, showing thereby the penetration of the ammonia. This 

 experiment, like the preceding, shows that the cuticle of normally 

 dried rotifers is not impermeable to gases and to water vapor and 

 that it therefore cannot protect the animals from desiccation. It 

 is quite possible and even probable that the cuticle, especially the 

 thicker part about the middle of the animal which covers it when 

 it is contracted, is useful in retarding evaporation. Experiments 

 to be mentioned below show that too rapid evaporation is injurious. 

 But although it may retard evaporation it cannot prevent it and it 

 seems certain, therefore, that so far as any external covering is 

 concerned there is no bar to complete desiccation of the animal. 

 That rotifers which have been exposed to conditions favoring 

 desiccation contain very httle water is shown by simple physical 

 methods. Spallanzani and Doyere both noticed that such rotifers 

 are so brittle that they break into pieces when pressed with the 

 point of a needle. The same result was obtained in the course 

 of these experiments and it was also observed that no water could 

 be obtained by exerting pressure on the cover glass covering the 

 rotifers, provided that the latter were examined immediately after 

 removal from the desiccator. When kept in a damp atmosphere 

 for a short time they absorbed sufficient water to be detected by this 

 method of treatment, and this probably accounts for the results 

 obtained by Davis, who claims to have been able to squeeze water 

 from rotifers which had been dried for three weeks in a vacuum, 

 since he admits that the water was obtained only after repeated 

 pressure had been applied. The fact that repeated pressure was 

 necessary at all shows that the amount of water present could have 

 been but slight, and it leaves room for the objection that there was 



