IIVDROTROPISMS OF FRESH-WATER INVERTEBRATES. 4! 



TABLE II. 



DRAGON-FLY NYMPHS. 



NORMAL CRAYFISH [Cambarus (Faxonins) propinquus 

 GIRARD] (PLATE II). 



In experimenting with the checker-board plate fourteen in- 

 dividuals were uscd.varying in length from one and a half 

 inches to three inches. In most cases the board was pl.n-l 

 within five or ten feet of the water, in some cases it was forty 

 feet from the water and, in a very few cases, it \\.i- fifty I < i 

 away. In most cases the experiments \\i-n- romluru-d lu-.ir tin- 

 river or brook from which the crayfish \viv ohtaiiu-d. In others 

 the crayfish were carried to the bonK-r- of some lake or pond. 

 The results are recorded in TabK- III. 



In an infinite series of experiment- t\v -nty-live per cent, of 

 movements toward the WUUT i> what >hoiill !> expected if the 

 water has not directive intluemv in the indi\ idnals. The ex- 

 periments yielded 67.5 of mo\munt- toward the water. Three 

 individuals made IOO per cent, of movement- toward the water, 

 four between 90 and loo per cent. In only four cases did the 

 per cent, fall under 50 and the lowest of those was 36. Evidently 



