THE KEY TO ANIMAL BEHAVIOR 



that could have been learned in no other way — 

 his demonstration, for instance, that certain phases 

 of tropism, response to external stimuli, is the same 

 in both animals and plants. His demonstrations 

 that life can go on without the nervous system, 

 that irritability and conductibility are qualities 

 of protoplasm, and that nature invented and im- 

 proved the nervous system to secure quicker and 

 better communication between the parts of an or- 

 ganism; the discovery that only "certain species of 

 animals possess associative memory, and have 

 consciousness, and that it appears in them only 

 after they have reached a certain stage in their on- 

 togenetic development " — that any animal that can 

 be trained, that can learn, possesses this memory: 

 all these things, and many others that Loeb has 

 found out by his laboratory experiments, throw 

 much light on the springs of animal life. It is not 

 an instinct that drives the moth into the flame; it is 

 a tropism — heliotropism. It is not an instinct that 

 makes a bedbug take refuge in a crack; it is another 

 tropism — stereotropism, the necessity of bringing 

 the body on every side in contact with solid bodies. 

 Professor Loeb has shown that neither experience 

 nor volition plays any part in the behavior of bugs 

 and worms; they are machines set going by outward 

 conditions. The warmth of the spring brings about 

 chemical changes in the bodies of caterpillars that 

 set them moving about. Wingless plant-lice, he says, 

 169 



