Effects of Desiccation on the Rotifer 253 



various cultures, it was found that in every case the period of maxi- 

 mum egg production had been preceded by a period of desicca- 

 tion and furthermore, that each desiccation of any length of time 

 had been followed by an increase in the reproductive activity. 

 This relation seemed to present so many points of interest that more 

 exact observations were made extending over a period of several 

 months. In addition, certain experiments were arranged in which 

 other factors which might have an influence on the result were 

 kept under control. The following is an account of the observa- 

 tions made on culture II during January, Febfuary and March, 

 1908. 



The culture was started in December, 1907. After being dried 

 several weeks, water was applied on January 2. Beginning with 

 January 8 differential counts were made every few days to deter- 

 mine the percentages respectively of eggs, newly hatched young, 

 and adults showing developing eggs. These counts were made 

 from random samples of fifty or more individuals taken from dif- 

 ferent parts of the dish. Although the results thus obtained could 

 from their nature be only approximate, the fact that several counts 

 made on the same day usually agreed very closely and that smaller 

 cultures in which the entire number of individuals could be observed 

 showed exactly the same changes makes it certain that the figures 

 given represent fairly accurately the condition of the culture as a 

 whole. In Fig. I the percentages of the different classes of indi- 

 viduals have been plotted as ordinates over the dates of observa- 

 tion and curves drawn to represent the changes that occurred in 

 the condition of the culture from day to day. The breaks in the 

 curves represent the periods of desiccation. 



Reference to the table will show that aside from a few irregu- 

 larities due to the entrance of the element of chance the curves 

 for the three periods show a general similarity. The curve rep- 

 resenting the number of egg containing individuals shows a maxi- 

 mum about four days after the application of water, that represent- 

 ing the number of eggs shows a maximum in each case after an 

 interval of six or eight days and that representing the number of 

 young atfer ten or twelve days. These figures agree closely with 

 those obtained where a small number of rotifers were kept under 



