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 craw] 
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 réle in 
this process are entirely unknown.’ 
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 Coccinelle for instance, are introduced into 
a closed wooden box (and are in addition kept in a dark 
room in order to shut out 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 
1J. SACHS, op. cit., p. 639. 
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