Effects of Desiccation on the Rotifer 255 



observation. The three maxima follow each other in regular 

 order, as should be expected, the maximum for the development 

 of the eggs w^ithin the body coming first, then that for the deposited 

 eggs, and finally that for the nev^ly hatched young. The two most 

 noticeable irregularities in the curves occur in the January series. 

 The first is in curve i where the maximum comes after the max- 

 imum of curve 2 instead of before it. This is probably due to the 

 fact that no records were kept between January 2 and January 8. 

 It they had been, a maximum in all probabiHty would have been 

 found during this period. The second irregularity, that in the 

 curve representing the number of eggs, on January 25, was due to 

 finding a cluster of five eggs, the eggs usually being laid in groups. 

 A careful search failed to disclose any more eggs and hence this 

 apparently high percentage did not represent a general condition 

 in the culture, being merely one of the errors of chance that con- 

 not be eliminated from a method of this sort. However, taken as 

 a whole, the curves show in a striking manner the relation between 

 desiccation and egg laying. 



It might perhaps be objected that inasmuch as the periods of 

 desiccation came at approximately equal intervals, their apparent 

 influence on egg production might be due merely to a chance 

 coincidence with a regular periodicity in the production of eggs 

 which is independent of external conditions. That this objection 

 has no force is shown by the fact that in other cultures dried at 

 very irregular intervals exactly the same results were obtained and 

 furthermore that in cultures allowed to continue for a long time 

 without drying no such periodicity -was observed. In one such 

 case the culture had not been permitted to dry for several months. 

 During the latter part of this period the percentage of eggs had 

 fallen almost to zero, it being a rare occurrence to find even a single 

 egg. The culture was then allowed to dry for two weeks. Ten 

 days afterward the percentage of eggs had increased to over fifty 

 where it remained for a few days and then again diminished until 

 a week or two later it was at zero. 



A number of experiments were made on small numbers of indi- 

 viduals. By keeping them in a fairly small drop of water in a 

 covered dish an accurate count could be made of the number of 



