Effects of Desiccation on the Rotifer 251 



ance it is plump and moist there are absolutely no traces of move- 

 ment either in the muscles or the contractile vesicle. The animal 

 is to all appearances dead, although the experiments mentioned 

 show that certian metabolic changes in all probability are occur- 

 ring. In the case of animals surrounded by even a very small 

 quantity of free v^^ater movements may frequently be observed 

 and the activity of the nephridia may often be clearly seen. In the 

 dried animal, while there are no movements of any sort, metabolic 

 changes must necessarily be very slow. It is possible, therefore, 

 that in the case of the rotifers surrounded by the moist air that 

 death may be caused by the fact that only a part of the functions 

 of the body continue while the others are suspended, metaboHsm, 

 for example, going on but the excretory organs being unable to 

 remove the waste substances set free. Perhaps, under these con- 

 ditions, owing to the impossibility of free interchange of liquids 

 between the different parts of the body, some of the organs are 

 especially affected by the metabolic changes that occur. Whatever 

 the nature of the processes with which we are dealing may be, it 

 seems certain that a state in which rapid chemical changes may 

 continue while some at least of the other vital processes have been 

 suspended is one of great danger to the animal. This danger may 

 be overcome either by reducing the chemical changes that occur 

 by further drying or by causing the resumption of the other vital 

 processes by the addition of a little free water. 



It is interesting to note that the suspension of many of the normal 

 activities of the animal occurs very suddenly. If a rotifer drying 

 on a clean slide be watched under the microscope and a drop of 

 water added at the instant when the last film of water surrounding 

 it is about to disappear, movements are seen to be resumed within 

 a few seconds; if the water be added a second after the film has 

 disappeared no movements occur for several minutes. The 

 actual amount of desiccation in the two cases is almost the same; 

 the effect produced is very different. As the last traces of the sur- 

 rounding water leave the animal there is a sudden suspension of 

 certain of the life processes. The suddenness of this suspension 

 as well as thfe fact that it occurs before actual drying of the tissues 

 of the animal has begun makes it probable that we are deahng 



