122 TROPISMS 



also in all probability of the suggestion that the apex 

 of a positively geotropic root has "brain functions." It 

 is chemical mass action and not "brain functions" which 

 are needed to produce the changes in growth underlying 

 geotropic curvature. 



2. As long as animals are in such a position that their 

 plane of symmetry goes through the center of the earth, 

 the position of their eyes and limbs is symmetrical in 

 regard to their plane of symmetry. If, however, we incline 

 the animal we can bring about forced movements and 

 forced changes of position of the same nature as those 

 caused by injury of one side of certain parts of the brain. 

 Thus we have seen that if we cut the left side of the 

 medulla oblongata in a shark, its two eyes are no longer 

 in a symmetrical position but the left eye looks down and 

 the right eye up, w T hen the shark is kept in a normal posi- 

 tion. The same change can be brought about in a normal 

 shark by the influence of gravitation. When the shark is 

 kept in a position with its right side inclined downward, 

 the right eye is turned upward, the left eye downward. 

 This has nothing to do with light or vision, since it occurs 

 in the dark just as well as in an illuminated room. The 

 abnormal position of the eyes lasts as long as the animal 

 is kept in this abnormal position. The experiment shows 

 that if the plane of symmetry is no longer vertical, forced 

 positions of the eyes can be produced of the same nature 

 as those produced by one-sided injury of certain parts of 

 the brain. 



Just as in the case of one-sided injury to the medulla 

 oblongata the changes in the position of the eyes are 

 accompanied by changes in the position of the pectoral 

 fins, so also when we put a normal shark with one side 

 downward or half downward. 289 If the right side of such 



