344 LOUIS MAX HICKERNELL. 



I. INTRODUCTION. 



The investigation upon which this report is based was begun 

 while the author was a graduate student in the Department of 

 Biology of Princeton University. A short summary of the 

 earlier findings has been published in a former article ('14). 

 The study of additional material and the completion of the 

 present paper has been carried out in the zoological laboratory 

 in the College of Liberal Arts of Syracuse University during the 

 last year. To Dr. E. G. Conklin, who first suggested this in- 

 vestigation to me, I wish to express my thanks for his interest 

 and for the many suggestions made at. various times during the 

 course of this study. I am also indebted to Dr. C. W. Hargitt 

 for many favors during the latter part of my work. 



The ability of certain rotifers, tardigrades and nematode worms 

 to withstand periods of desiccation has been a subject of investi- 

 gation for many biologists throughout a period of more than 

 two hundred years. The first recorded observations upon desic- 

 cation phenomena are those of von Leeuwenhoek in 1701. From 

 the gutter of a roof he took some dust which he moistened and 

 examined with his microscope. He observed living animals 

 swimming about actively in the water. He found that the 

 animals, which were, no doubt, rotifers, could be deprived of 

 moisture for many months and could then be revived by the 

 addition of water. 



After the work of von Leeuwenhoek, the problem of the 

 drying of living things was forgotten for a time. It was not 

 until the period between 1750 and 1775 that interest in the 

 study of desiccation phenomena was revived. During this 

 quarter century many forms were added to the list of animals 

 capable of enduring desiccation. 



In 1776 Spallanzani discovered certain tardigrades and nema- 

 todes which were able to endure desiccation. He worked also 

 on rotifers and was the first to state that rotifers, w-hen dried 

 free from sand, could not recover from the effects of the drying 

 process. The failure of Spallanzani's rotifers to recover has 

 since been shown to be in no way due to the absence of sand but 

 his experiments aroused much discussion and engaged the atten- 

 tion of many of the foremost naturalists of that day. 



