HVDROTROPISMS OF FRESH-WATER INVERTEBRATES. 43 



These experiments yielded 18.8 per cent, of movements in the 

 direction the head originally pointed. This is so near to what 

 theory demands that it is evident that the original position of 

 the head has not appreciably influenced the final movements of 

 the individual. 



In tin- matter- con-idered no marked difference was observed 

 In -t\\een male- and females. 



At the close of each series of experiments mentioned above, 

 t In- crayfish wa- placed on the ground, with its head away from 

 the water. The distances from the water ranged from ten to 

 fifty feet. In each case the crayfish finally turned and went to 

 the water, even going around obstacles. 



On another occasion twelve crayfish were placed, one at a 

 time, on the ground, within ten feet of the body of water from 

 which they had been obtained. They were always faced away 

 !n>m the water. Kleven of these reached the water in a very 

 few minutes; the twelfth roamed about for fully half an hour 

 before- it found the water. Considered alone these experiments 

 uonld not permit us to draw any conclusions. The land sloped 

 io\\.ird the water. The sun was shining. Hence gravity and the 

 -mi rays may have influenced the movements. However, the 

 results are in harmony with the conclusions drawn from the ex- 

 periments on the checkerboard plate; and, when considered in 

 conjunction with some experiments to be described in the next 

 section, they are illuminating. 



Bi INDED CRAYFISH (Cambaraus sp.? AND Cambarns (Fraxoni 

 propinquus Girard) (PLATE III). 



The above experiments with the checkerboard plate prove 

 conclusively that the nearest body of \\ater. in -onie manner, 

 forces the crayfish to move toward?- it. < >ne naturally \\onders 

 if the eyes function in this behavior. To te-t the matter three 

 types of experiments were conducted \\ith blinded na\ii>h. 



In the first series thirteen blinded < Ta\ \\-\\ \\ere te-ied on the 

 checkerboard plate. The e\e> of li\e \\ere Minded with an 

 opaque varnish, the eyes of the other eight wvre amputated. 

 The board was placed twenty feet from the water. The ronlt> 

 are recorded in Table IV. 



In an infinite >erie- of experiments, if the factors considered did 



