68 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



surface of the water. It can be shown, however, that 

 this is not the case. If a large beaker filled with 

 water be placed inverted in the aquarium, the Cucu- 

 mariae that are under the beaker begin to creep up to 

 the bottom of the glass. They also do so when the 

 experiment is made in the manner represented in Fig. 

 19. A bridge B B is placed in the aquarium A A, 

 the horizontal part of the bridge B B being below 

 the surface of the water of the aquarium. The hori- 

 zontal part has a round opening o over which the in- 

 verted beaker abed filled with water is placed. Fresh 

 water is supplied at a low pressure at o through a 

 glass tube^, which has been properly bent. The Cu- 

 cumariae nevertheless go away from o and remain at 

 the highest point c d, or near cd on the vertical sides 

 (Fig. 19), where they ultimately die. 



Experiments on the centrifugal machine yielded no 

 result, for the animals did not move during the rota- 

 tion. Gravity is the only condition which can account 

 for the phenomenon, and I imagine the influence 

 which gravity exercises to be in a manner similar to 

 that observed among insects for example, in butter- 

 flies which have just emerged from the chrysalis. 

 The wings of the butterfly do not unfold immediately, 

 and it runs about restlessly until it comes to a vertical 

 surface. When this is reached, the butterfly creeps 

 upon it and remains there for some time with its head 

 up. After the wings are spread, other conditions 

 cause the animal to be restless again. 



Because of this dependence on gravity, the Cu- 



