262 J. E. WODSEDALEK. 



varying in size so that the space gradually varied in thickness from 

 one end to the other. Then a large number of specimens were 

 put in the water and after a short time it was found that nearly 

 all of the specimens were attached to the lower surface of the 

 upper brick with their dorsal sides downward, and a large major- 

 ity of the specimens were in that part of the wedge-shaped space 

 where their backs came in contact with the brick below." The 

 operated specimens in their wandering about over the surface 

 of the stone accidently came into such a place where their backs 

 came in contact with the floor of the basin. This stimulus 

 naturally appealed to their thigmotactic propensity and hence 

 the greater tendency to remain on that portion of the rock. It 

 seems only natural, therefore, that an association would be 

 formed between this more satisfactory environment and the 

 lower surface of the stone. It is not altogether improbable how- 

 ever, that such a habit had already been partially formed before 

 the operation took place. 



Further evidence for the fact that this thigmotaxis is largely 

 responsible for the gradual disappearance of the insects from the 

 upper surface, is apparent from the results obtained in some 

 checking experiments. In those experiments the stone was sus- 

 pended in the water so that the backs of the nymphs could not 

 come in contact with other objects. The results were surprising 

 and all remaining doubts as to the function of the Palmen's organ 

 in the nymphs were resolved. As long as the experiment was 

 continued the specimens remained quite evenly scattered over 

 the entire surface of the suspended stone. A similar experiment 

 was tried with the normal specimens, also in the dark chamber, 

 and practically all of the specimens remained exclusively on the 

 lower surface. It is only natural, then, to conclude that Pal- 

 men's organ has a great deal to do with the orientation of these 

 insects. That this unusual behavior is not due to the shock the 

 insects receive from the operation was proven by the fact that 

 when other parts of the head and body were destroyed no com- 

 parable results in behavior took place. 



Although the foregoing results are thoroughly convincing as 

 to the function of the organ in these nymphs, further results of 

 observations on behavior relative to the role of the organ may 



