GEOTROPISM IN ANIMALS 179 



and rather quote^the words with which J. Sachs describes 

 the geotropism of motile plants: 



I have already called attention to the remarkable way in which 

 Plasmodia crawl up the stems of plants, flower-pots, and other 

 comparatively high objects. They can be induced to do this most 

 readily when moist glass plates are fixed vertically into tan bark 

 containing young Plasmodia which are just ready to creep to the 

 surface. In the course of a few hours the mesh-like bodies crawl 

 to the highest points of the glass plate, which can now be removed 

 and observed directly under the microscope in order to watch their 

 movements more accurately. It can scarcely be doubted that this 

 impulse to crawl upward is to be considered the effect of a 

 geotropic stimulus; that is to say, that an as yet unknown effect of 

 gravitation upon the molecular structure of the protoplasm influences 

 the movements of the molecules in such a way that the effect which 

 we have described is finally brought about. It is scarcely necessary 

 to add that the individual mechanical factors which play a role in 

 this process are entirely unknown. 1 



Others dispute the idea that the Plasmodia are geotropic. 

 They claim that these phenomena are the expression of a 

 rheotropism and hydrotropism. 



I showed in one of my earlier papers that certain insects 

 behave in a way analogous to the movements of Plasmodia. 

 In the case of insects these movements are certainly not 

 dependent upon rheotropism and hydrotropism. If certain 

 insects, such as Coccinellse for instance, are introduced into 

 a closed wooden box (and are in addition kept in a dark 

 room in order to shut oat every effect of light), they have a 

 tendency to creep up the vertical walls of the box and to 

 collect in the highest regions. The behavior of these 

 animals toward gravitation corresponds with that which 

 Sachs has described for Plasmodia. 



A similar phenomenon is noticed in marine animals. In 

 this connection it contributes toward the understanding of 

 bathometric distribution of these animals. The reader is 



ij. SACHS, op. cit., p. 639. 



