4O C. H. TURNER. 



board marked O, always faced the water. If there had been an 

 unlimited number of experiments, twenty-five per cent of 

 movements toward the water would indicate that the movements 

 were random and not influenced by the position of the water. 

 Since the number of experiments was limited to about 500, 

 unless the movements toward water were much more than twenty 

 five per cent, the movements were considered random. In 

 recording movements toward the position of the sun and the 

 initial position of the insect's head, eight possible directions 

 were considered. In each of these cases, if there had been an 

 infinite series of experiments, 12.5 per cent, of movements in a 

 certain direction would indicate random movements. Hence, 

 since there were only about 500 experiments, unless the per cent 

 of movements in a certain direction was much more than 12.5 

 the movements were considered random. 



With the animals investigated in this connection, in addition 

 to the experiments with the checker-board plate, the creatures 

 were set free, at definite distances from the water, and their 

 movements watched. If the experiments demonstrated a tend- 

 ency to move toward the water, then the specimens were blinded 

 and the experiments repeated. 



DRAGON-FLY NYMPHS (PLATE I). 



In experimenting with the checker-board plate fourteen 

 individuals were used. In some cases the board was ten feet from 

 the water; in others it was fifteen. Five hundred and fifty-six ex- 

 periments were performed. The results are recorded in Table II. 

 In an infinite series of experiments, if the factors considered 

 did not influence the movements in any manner, 25 per cent, of 

 the movements should be toward water, 12.5 per cent, toward 

 the position of the sun and 12.5 per cent, to the way the head 

 originally pointed. The actual results were 25 per cent toward 

 water, 20.5 per cent, toward the position of the sun and 23.3 per 

 cent, toward the way the head originally pointed. Only tlmv 

 individuals made more than thirty per cent, of movements to 

 water. Evidently, dragon-fly nymphs, when moving about on 

 the checker-board plate are not influence by the nearness of 

 bodies of water. 



