222 Merkel Henry 'Jacobs 



side of the dish away from the Hght where they could be removed 

 by means of a fine pointed pipette. If left undisturbed for thirty 

 or forty minutes they again spread out into all parts of the dish. 



2 Behavior at the Onset of Desiccation 



At the onset of desiccation, no matter under what circumstances 

 it occurs, the animals all show a general restlessness. If they have 

 been quietly feeding, for example, they withdraw the corona and 

 begin to make active creeping movements. These movements 

 are more or less at random and thus differ from the responses 

 made when creeping, to more definitely localized stimuli. The 

 negative phototaxis, which is shown so markedly under certain 

 conditions, is always abandoned when the water begins to dis- 

 appear. A group of rotifers which has collected on the side of the 

 dish away from the light is quickly broken up, each individual 

 starting to creep in the direction in which it happens to be turned 

 at the time and continuing in this direction until it comes either 

 to the edge of the drop or to a place where the surface film lies so 

 close to the slide that it cannot creep under it. It then stops, 

 contracts, makes one or two testing movements with the proboscis, 

 and starts off again in a new direction until brought to a stop in a 

 similar way. Contact with sohd objects such as grains of sand 

 does not cause the creeping movements to cease as Davis and 

 others have assumed. So far as can be observed the behavior 

 of rotifers dried on a clean slide and those dried with a quantity 

 of sand is essentially the same. In both cases they continue to 

 creep as long as it is possible to do so and when such movements 

 become impossible they contract into a more or less spherical mass 

 and dry wherever they happen to be. As has been mentioned 

 the movements are purely at random. Frequently a number of 

 rotifers may be seen in the field of the microscope at once, all 

 creeping in different directions. When two rotifers meet they pay 

 no attention to each other but continue on their way just as before. 

 There is no instinct that leads them to gather together in groups 

 for mutual protection as Hudson and others have asserted. Where 

 such groups are found the cause is merely that they have all re- 



