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 Palaemon. In moulting, the lining of the statocysts 

 is cast off and the statoliths or small particles of sand they 



