MOVEMENTS OF THE EARTHWORM 619 



portion, and a muscular contraction-wave runs forward there- 

 from. Strong stimuli may cause a more violent reaction, where- 

 upon the worm will commence to creep and both parts, on either 

 side of the inactive " nerveless" region, behave in a coordinated 

 manner. 



When, however, the stimulus is applied to the extreme posterior 

 end, a much more vigorous reaction is generally obtained. The 

 muscular contraction-wave, either starting at the most posterior 

 point, stops abruptly at the " nerveless" part, or else, beginning 

 immediately behind the "nerveless" area as a constriction of the 

 body-wall runs backwards. But in no case does the impulse pass 

 across the " nerveless" part. 



From what has been said in the foregoing, it seems clear that 

 muscular contractions in some part of the worm, unless very 

 strong, are insufficient to induce a state of muscular activity in an 

 adjacent part; and, as a matter of observation, locomotion consists 

 of alternate lengthening and shortening of successive groups of 

 segments. 



Friedlander was surely aware of the fact that at times the earth- 

 worm behaves not as a series of individual segments but unmis- 

 takably as a unit. Such behavior, however, he believed to be 

 peculiar of reaction to special stimuli, but not of ordinary quiet 

 locomotion. "Esist wahrscheinlich, dass der Regenwurm — und 

 wahrscheinlich auch andere Anneliden — nicht als einheitliche 

 Individuen, sondem vielmehr sozusagen als Segmentreihen kro- 

 chen, so lange keine besonderen Reize auf sie einwirken" (p. 202). 



It will be my task in the following to demonstrate, that in quiet 

 creeping, just as in the exceptional instances of strong stimulation, 

 the principle of totality of the organism asserts itself very decid- 

 edly. This brings me to the consideration of the second problem, 

 namely, what determines the earthworm's movements in a definite 

 direction? 



Although this problem lias been studied extensively, the true 

 nature of the worm's orientation in space must necessarily have 

 remained an unknown quantity so long as the sole purpose of the 

 investigations has been the discovery of the directive influence 

 of stimuli. As far as 1 know, Jennings was the first to insist 



