57^ Journal of Comparative Neurology and Psychology. 



tion, some form of shrinking movement followed by forward creep- 

 ing. But if all such cases are plotted together, it is found that they 

 form two curves and this is the basis for calling them distinct reac- 

 tions. It was pointed out in the description of type V that some of 

 those reactions consisted of a single quick turn end for end and that 

 this movement differs only in extent and intensity from type II. It 

 is quite immaterial whether such a reaction is classed under II or V, 

 since all gradations are found between the two types. If an attempt 

 is made to keep them distinct, the two curves slightly overlap. 



The Tropic Tendency in the Different Reaction Types. — In a 

 second table is given the data on direction of turning in the different 

 types. It is seen that about 70 per cent of negative turns were 

 recorded in types I to III. There is a falling off in the case of V to 

 60 per cent, but quite a large numl>er of undetermined cases are 

 included. Type V is a movement of such swiftness that there 

 is greater difficulty in its observation. That is not the case in the 

 other types to nearly the same extent, for the negative turning occurs 

 in types III and IV at the beginning of resumption of forward 

 movement after a period of backward crawling, and the necessary 

 pause in the movements of the worm at such a time makes it usually 

 possible to determine the direction of turning. This is of course 

 especially true when there is some approach to circus movements, 

 as it sometimes happens that the turning is repeated a number of 

 times. When the worm begins to move forward at once after the 

 initial phase, it crawls more rapidly and the tendency to crawl 

 straight forward is sometimes marked. Sometimes the tropic tend- 

 ency appears after the worm has quieted down somewhat, but owing 

 to its doubtful character in such cases they were classed as a rule as 

 undetermined. 



It should be emphasized that the tropic tendency is a feature that 

 appears after the period of excitement due to the stimulus has sub- 

 sided or else as the primary response to a very weak stimulus. Jen- 

 nings in a recent paper ('06) takes the general position that the tropic 

 reaction in the case of the earthworm is only one feature and that a 

 subordinate one of a complex behavior. It may be added that as a 

 feature of the complex responses it may often disappear or appear 



