

 PALMEN'S ORGAN IN HEPTAGKNIA AND ECDYURUS. 263 



be cited. When the specimens are collected and dropped into a 

 dish of water many of the individuals fall to the bottom with 

 their ventral sides upward. This toppling over is even more 

 obvious when the specimens are placed in a dish of water in \ir 

 a light. In their attempts to get away from the light and 

 repeatedly clawing at the opposite end of the <li-h tin- spedniens 

 become exhausted and very frequently when the clavvin- move- 

 ments cease the apparently lifeless individual* fall to the 1 >< >\[\\\, 

 dorsal side downward. This period of re>t t >rr< '-ponds some- 

 what to the death-feigning instinct of the insect. By \ i-onm-ly 

 stirring up the specimens or throwing them into water havii 

 temperature to which the specimens are not aivn-tonied. or into 

 relatively strong chemical solutions of various son-, a- adds. 

 salts, alcohol, etc., practically all of the specimen- tall into this 

 momentary, rather stiff, inactive state and slowly <! -< -ml to the 

 bottom of the dish. In so doing almost all of the specimens 

 topple over and fall down head-first, ventral side up ami on the 

 average, at an angle of about 45 degrees. It ini^lit al-o In- 

 mentioned here that nymphs which are found dead in the aquaria 

 lie almost invariably with their ventral side up. ( >n the oilier 

 hand, the turning over is under similar conditions far le-- frequent 

 among the specimens from which the organ had been remo\ed. 

 It two groups of freshly killed specimens are taken, all <>l which 

 have been cleaned and their appendage- arranged, the one i^roup 

 normal in every way, the other having the I'.ilnn-n'- organ re- 

 move.d. we find by allowing them to de-rend through a d 

 jar of water that almost invariably the li-rnier topple o\cr and 

 -ettle on the bottom ventral side up, while the latter eqnallv as 

 frequently reach the bottom and remain there \\iih thdr \entral 

 side downward. 



CONCLUDING RIMAK; 



The results of the foregoing experiments show conclusively 

 that the organ, as small as it is, plays a very important role in 

 the behavior of the nymphs upon which these experiments v, 

 performed. This is doubtless due to the weight of the chitinous 

 ma-> whose pressure seems, to a large extent, to control certain 

 orientation of the in-ects. Gross (1903) gives a figure of the 



