Effects of Desiccation on the Rotifer 227 



acter. In certain cases they failed to observe the recovery of 

 dried rotifers and they, therefore, conclude that such recovery 

 is impossible. On the other hand, many observers have con- 

 tributed an abundance of positive evidence, of which that just 

 given is typical. It is possible for anyone, by using the proper pre- 

 cautions, to dry rotifers and see for himself the gradual return 

 of movements up to the time of complete recovery. It is certain, 

 therefore, that the return of all of the normal vital activities in 

 animals which by drying have been rendered motionless and 

 apparently lifeless is not one of the myths of zoology as many have 

 supposed. This does not imply that the rotifers which have been 

 subjected to the conditions of dryness have actually undergone 

 a true desiccation. From the evidences so far presented it is 

 possible that they have not. This point will be discussed more in 

 detail in the next section. 



It is necessary to observe that all rotifers are not equally resist- 

 ant to a process of drying. The only well authenticated cases of 

 recovery after desiccation are found in the family Philodinidae 

 (Philodina, Rotifer and Adineta) in species which normally Hve 

 in places where they are exposed to drying at frequent intervals. 

 Perhaps other rotifers possess this power, but that such is the case 

 has not been proven. A number of experiments made to deter- 

 mine this point with Megalotrocha and several of the Loricata 

 gave purely negative results, no cases of recovery being observed. 

 The observations of Lance ('94) are of interest in this connection. 

 He found in the tardigrades that only those species could resist 

 desiccation which live in places where they are exposed to it under 

 natural conditions. 



VI DEGREE OF DESICCATION ATTAINED BY PHILODINA 



One of the most disputed points in connection with the entire 

 subject of suspended animation in rotifers and other aquatic ani- 

 mals is the degree of desiccation they may attain without injury. 

 Some workers hold that there is no limit to the amount of drying that 

 may occur, while others just as strongly contend anything resem- 

 bling a true desiccation is necessarily fatal. They believe that in 



