GEOTAXIS 31 
Cormyorpha (Torrey)—geotropism is manifested in the 
direction of growth much as in the higher plants. 
Among the worms geotactic migrations are manifested by 
Convoluta and were found by Bohn to vary with the tide 
as is described in another connection (Chapter VII). Des- 
truction of the statoliths in this form was found to destroy 
its reaction to gravity. The sea-cucumber Cucumaria 
cucumis is described by Loeb as having a marked tendency 
to crawl upward. The upward migration occurs as well in 
inverted glass cylinders, showing that it is not the supply 
of oxygen which attracts the animal to the upper surface. 
A tendency to vertical migration is shown by many free 
swimming crustacea. In the copepod Labidocera Parker 
observed that the females showed a marked negative geo- 
taxis in the dark, but when exposed to light their geotaxis 
became positive. Whether they were illuminated from above 
or below did not alter their response. Although negatively 
phototactic they nevertheless swim downward when light 
falls on them from below. 
Many crustaceans have statocysts which are especially 
concerned in the maintenance of equilibrium. In Mysis 
they are located in the inner branch of the caudal appendages. 
Delage found that if these organs were destroyed the animals 
had difficulty in maintaining their equilibrium, which was 
further increased by the destruction of the eyes. In the 
decapod crustacea the statocysts are situated in the basal 
joint of the antennules. Destruction of these organs is 
followed by a variable degree of loss of equilibrium in differ- 
ent species. 
The most instructive and ingenious experiments in the 
functions of the statocysts were performed by Kreidl on the 
prawn Palemon. In moulting, the lining of the statocysts 
is cast off and the statoliths or small particles of sand they 
