REACTIONS OF PLANARIA TO WATER. 123 



among the different tests. But in some experiments the lot of 

 worms gave consistent results directly opposite to those generally 

 obtained. Thus in the experiments of lowering the temperature, 

 five of the seven tests in which the positive reaction remained 

 unchanged were the successive tests in a single experiment. 

 In this case the temperature at the beginning of the experiment, 

 and the amount of the depression of the temperature, were the 

 same as in other experiments in which reversal of reaction was 

 produced in the characteristic manner. Such differences in 

 behavior must be attributed to that complex of internal pro- 

 cesses which has been characterized the "physiological state" 

 of the organism. 



VII. REACTIONS TO CURRENTS OF WATER IN NATURE. 



That rheotropic reactions are normal to the life of planarians 

 in nature is shown by field observations. The specimens studied 

 in the laboratory were collected in a spring-fed marsh at the 

 edge of the Fox River near Chicago, called "Station 10 Cary 

 Spring" in Shelford's description of the animal communities of 

 the Chicago Region (Shelford, '13, pages 52, 93 and 118). The 

 marsh bottom is composed of black humus without stones under 

 which the worms could collect in the manner that Pearl found 

 characteristic of this species in the Huron River, but an abundance 

 of leaves serves the same purpose. The water is very shallow 

 and well shaded by marsh vegetation. There is a sluggish current 

 fed by springs at the upper edge of the marsh, where water cress 

 is found growing. 



A small channel about five inches wide and fifteen feet long 

 was discovered at the edge of the marsh through which a moder- 

 ate current of water was flowing. A large number of worms were 

 found in this stream, some moving on the bottom, generally 

 up-stream, but most of them at rest on the under sides of leaves 

 or in sheltered places on the bottom. Removing the shading 

 vegetation for better observation stimulated many of the worms 

 at rest to become active, and half an hour later 60 worms were 

 counted going up-stream and 5 going down-stream and 200 were 

 counted at rest on the under side of leaves. At that time the 

 sun was shining somewhat from the side, and down-stream, but 



