THEORY OF INSTINCTS 185 



plates which rested on small blocks, and were raised 

 just enough from the bottom to allow an Amphipyra 

 to get under them. Then the Amphipyra collected 

 under the little glass plates, where their bodies were 

 in contact with solid bodies on every side, not in the 

 dark corner where they would have been concealed 

 from their enemies. They even did this when in so 

 doing they were exposed to direct sunlight. This re- 

 action also occurred when the whole box was dark. It 

 was then impossible for anything but the stereotropic 

 stimuli to produce the reaction. The same phenom- 

 enon may be observed in worms, for instance, in 

 Nereis. If an equal number of Nereis and glass tubes 

 be placed in a dish of sea-water, we may be sure 

 that after a time we shall find a worm in each tube. 

 This even occurs when the tubes are exposed to the 

 direct rays of the sun, which kill the worms. This is 

 also a reaction which is common to plants, hydroids, 

 and animals possessing a central nervous system, 

 which must therefore depend upon circumstances 

 which have nothing directly to do with the central 

 nervous system. These circumstances are apparently 

 chemical effects in the skin, which are produced in 

 these forms by the contact with solid bodies. This is 

 another instance where the central nervous system 

 only plays the part of a protoplasmic conductor. It 

 would be entirely wrong to attempt to look for a 

 " centre of self-concealment " in these animals. This 

 is confirmed by experiments on worms that have been 

 cut into pieces. 



