148 C. H. TURNER. 



maze from the ground always moves upwards, while one placed 

 on the tip of the maze always moves downward. It is not neces- 

 sary to postulate a negative geotropism to explain one and a 

 positive geotropism to explain the other, and puzzle our brains 

 to account for the reversal of the tropic response when the insect 

 is bodily transported from one place to the other. The behavior 

 is not a tropism. When the caterpillar nears the foot of the 

 maze, the exploring movements which it invariably makes when 

 it nears a change in its environment would cause it to first en- 

 counter the post with its head pointed upwards. When placed 

 on the top of the maze, if its movements bring it in contact with 

 the side of the post, it will inevitably be with the head of the 

 insect pointing downward. In one case the insect ascends, in 

 the other it descends; in neither case is the predication of a 

 tropism necessary to explain the behavior. 



CONCLUSION. 



Evidently there is nothing about the behavior of surface- 

 feeding caterpillars which warrants the assumption that their 

 locomotions are tropisms. The movements made in locomotion 

 are identical with those made by animals that learn by the trial 

 and error method. Instinctively the caterpillars are physiologi- 

 cally attuned to a certain environment. Outside of that en- 

 vironment there is physiological unrest. To escape the unpleas- 

 antness of its environment, the creature makes random move- 

 ments similar to those made by creatures that learn by the trial 

 and error method. There is no automatic adjusting of the body 

 so as to have it symmetrically stimulated by an external excitant. 

 Some internal, instinctive stimulus causes it to move ahead until 

 some sensation factor induces it to change its course. If phys- 

 iological satisfaction is not obtained, it continues its random 

 movements until fatigue causes it to rest. Evidently the loco- 

 motions of surface-feeding caterpillars need to be classified with 

 trial and error movements rather than with tropisms. 



It must be distinctly understood that nothing stated above 

 refers to recently hatched caterpillars, nor to larvae immediately 

 before entering the pupa state, nor to caterpillars (like the codd- 

 ling moth larva) which feed inside of plants. Their behavior is 

 left for a future discusions. 



