Effects of Desiccation on the Rotifer 209 



is the condition of the dried animal ? Are its hfe processes merely 

 retarded or have they come to a complete standstill ? In the 

 revival of a dried animal by the apphcation of v^ater, are w^e deal- 

 ing, as many have supposed, v^ith a case of passage from death to 

 life or merely w^ith an acceleration of vital processes which have 

 been continuing all the while but in a greatly reduced state ? 



These and similar questions have been under discussion for 

 many years and as yet no unanimity of opinion has been reached 

 by zoologists in regard to them. Every point has been affirmed 

 and denied many times by equally capable men. Much of the 

 discussion on the subject has been pure speculation based on 

 neither observation nor experiment and hence is of little value; 

 however, even the most careful observers have differed radically 

 with each other on many points of importance, the observations 

 of one worker being contradicted by the apparently equally accu- 

 rate observations of another worker. The result is that the ques- 

 tion even at the present day is in a state of the greatest confusion 

 and uncertainty and is still far from being finally settled. 



It was with the intention of clearing up some of these points of 

 dispute that the present piece of research was undertaken in the 

 fall of 1906 at the suggestion of Prof. E. G. Conkhn. It gives me 

 great pleasure to express at this point my sense of deep indebted- 

 ness to him not only for suggesting the subject but for the inter- 

 est he has taken in the work^and for the many helpful suggestions 

 and criticisms he has offered. The experiments were performed 

 in the Zoological Laboratory of the University of Pennsylvania 

 during the years 1906-1907 and 1907-1908, During the course 

 of the work a number of points of interest somewhat off of the 

 main line of the investigation came up; some of these points are 

 touched upon in the present paper, others are still under investi- 

 gation and are reserved for subsequent pubHcation. 



The animal worked upon was Philodina roseola, one of the 

 Bdelloid rotifers, and in all cases except where otherwise expressly 

 stated it will be understood that the observations apply to this 

 form. Philodina was chosen partly on account of the ease with 

 which it could be obtained, making experiments on large numbers 

 of individuals possible, and partly because it shows the phenom- 



