56 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



the ulva leaf will at any time leave the glass and 

 attach itself to the leaf, the reverse is not liable to 

 happen. This contact-irritability of the foot does not 

 change if the head or the greater oral part of the ani- 

 mal be amputated. The mechanisms for the discharge 

 of these reactions must, therefore, be located in the 

 foot itself and not in the ganglion-cells of the oral disc. 

 5. I n higher animals we recognise a tendency to give 

 the body a certain orientation in space. We usually 

 call such an orientation in a higher animal its position 

 of equilibrium. Certain Actinians also show such phe- 

 nomena. If we put a Cerianthus into a test-tube 

 filled with sea-water, and place the glass so that the 

 head of the animal is down, the foot up, and the long- 

 itudinal axis vertical, the tip of the foot will begin 

 after a few moments to bend downward vertically. 

 In Fig. 13 the course of such an experiment is given 

 from life. Some minutes before 12 o'clock the ani- 

 mal was placed in the test-tube in the manner de- 

 scribed above. At 1 2 o'clock the foot had begun to 

 bend downward (Fig. 13, a) ; in the next thirteen 

 minutes the bending toward the head had progressed 

 (fr) ; five minutes later the foot had reached the bot- 

 tom of the tube (c). The bending progressed steadily 

 to new elements lying near the head ; and since the 

 foot now stood upon the bottom of the tube, the 

 farther advance of the curvature toward the head 

 resulted in the lifting of the latter (Fig. 13, d and e), 

 whereupon the animal raised itself bodily, and at i 

 o'clock had the position f. The process of righting 



