Spatially Determined Reactions 163 



geotropism induced by the light was of sufficient influence 

 to make them move downward toward it (113). Other 

 facts regarding the relation of geotropism and phototropism 

 are mentioned on pp. 182 ff. 



63. Orientation to Gravity: Spiders and Insects 

 | Spiders and insects have no statolith organs. Bethe 

 ^thinks that equilibrium is maintained in their case as a 

 natural result of the position of the centre of gravity and the 

 distribution of air in the body. He supports this view by 

 experiments in which dead insects, allowed to fall through 

 the air, assume the normal position, and is inclined to think 

 that all animals without special static organs maintain their 

 balance in this way (27). Negative geotropism in certain 

 insects, as evidenced by a tendency to creep from horizontal 

 planes up vertical ones, was observed by Loeb (234). In 

 light the eyes of insects have probably much to do with 

 maintaining equilibrium. Certain aquatic insects, in ex- 

 periments where the light was made to strike them only 

 from below, as soon as they left the support on which they 

 were resting, turned themselves upside down (355). 



64. Orientation to Gravity: Vertebrates 

 It has long been known that in vertebrates the static 

 function resides in the ear, and especially in the semicir- 

 cular canals (e.g., 70, 85, 128, 147). Various experimenters 

 have noted that operations on the ears of fishes disturb the 

 equilibrium of these animals. Sewall, indeed, found that 

 section of the semicircular canals in the shark had no effect 

 on its balancing powers, although operations on the vesti- 

 bule and ampullae did disturb movement (380) ; and 

 Steiner got no effect on equilibrium from removing the 

 contents of the labyrinth (391). Errors in method and 



