260 J. E. WODSEDALEK. 



took place, nor was there a union formed between the different 

 tracheae Fig. 2 is of a specimen in which the trachea? were 

 broken at quite a distance from the organ; again, no growth 

 beyond the covering over of the broken ends and the formation 

 of a few small tubules took place. 



COMPARISON OF THE BEHAVIOR OF NORMAL AND OPERATED 

 SPECIMENS IN RELATION TO THE FUNCTION OF 

 PALMEN'S ORGAN. 



In my previous papers (Wodsedalek, 'n and '12), the behavior 

 of H, interpunctata nymphs has been discussed in considerable 

 detail, and hence only the more important phases of the behavior 

 of this insect which directly concern this problem will be cited 

 here. The nymphs are decidedly negative in their phototactic 

 response in all gradations of light, varying from ordinary day- 

 light to very intense electric illumination. Their thigmotactic 

 propensity, or tendency to come in contact with and cling to 

 objects, is especially pronounced. In their natural environ- 

 ment the nymphs are never seen swimming freely about in the 

 water, even when observed in their favorite places in which 

 they occur in great abundance. In their natural habitat they 

 are always found clinging to the under surfaces of small rocks, 

 and this same position is regularly assumed by all normal ones 

 in the aquaria of the laboratory. When a stone, to which the 

 specimens are attached is inverted in the water, the insects 

 soon make for its under side, many of them doing this as the 

 stone is being turned over. This is also true of normal specimens 

 in the dark-room, and hence it is obvious that this tendency of 

 the nymphs to cling to the lower surfaces of rocks, with their 

 dorsal side downward, is not due entirely to their negative reac- 

 tion to light. It is unquestionably due, in part, to a definite 

 power of orientation independent of phototaxis. 



Specimens from which the Pill men's organ was removed 

 react to light in practically the same way as do the normal 

 specimens. Their thigmotactic inclinations, too, do not seem 

 to be impaired. However, when the insects are taken into a 

 very shaded or a dark-room the difference in orientation becomes 

 quite obvious. When a stone to which the insects are attached is 



