No. 502] THE DESICCATION OF ROTIFERS 671 



brought about by removing the eggs from a somewhat 

 foul and cencentrated culture to fresh spring water. 



This process of causing winter eggs to develop in the 

 summer is very likely the same that occurs in nature in 

 the spring months. During the fall and winter the pools 

 become free from abundant animal and plant forms and 

 the accompanying products of decomposition by the fre- 

 quent floodings by rains and the low temperature. In 

 the spring the heavy rains flood the pools again and the 

 osmotic pressure of the water is so much lower than it 

 was in the previous summer that the eggs absorb water 

 enought to rupture the thick outer membrane and stimu- 

 late the embryos to growth. As the temperature becomes 

 favorable they develop and the life cycle is completed. 



From the foregoing observations it seems probable 

 that desiccation of the adult rotifers followed by revival 

 is not of widespread occurrence in the group and is not 

 the means resorted to by most species for tiding over 

 unfavorable periods. Survival is due in most cases to 

 the winter eggs which can withstand both desiccation and 

 a low temperature. 



