THE REACTIONS OF LOWER ANIMALS. 239 



a needle, or otherwise slightly stimulated, may be thrown into 

 violent jerking and squirming motions. According to Loeb we 

 have no more right in this case to conclude that these motions 

 are due to pain-sensations than we have to make a similar con- 

 clusion upon the contractions of an isolated frog's muscle when 

 put into a too concentrated salt solution. My experiments 

 upon the earthworm clearly prove that this view in contrast to 

 that of the pain-sensations is the correct one. 



It has already been observed that if we attribute feeling to 

 the earthworm because of certain reactions, we must do like- 

 wise for any isolated piece of the worm ; and, further, that the 

 front half of any such piece must have a state of feeling differ- 

 ent from that of the posterior half. But since the piece to be 

 experimented upon may be taken from any part of the worm, 

 the front half could as easily have been the posterior half, and 

 vice versa. Hence it follows that the nature of the reaction of 

 any given piece of the earthworm is a function of the direction 

 of the impulse. If the impulse travels from the injured spot 

 anteriorly, the piece of worm elongates ; this initiates the nor- 

 mal progressive movements ; if the impulse travels from the 

 injured spot posteriorly , the piece of worm executes the charac- 

 teristic jerking and squirming motions. In the first case the 

 circular muscles are the first to contract, and this causes the 

 elongation of the piece ; in the second case the longitudinal 

 muscles are the first to contract. This causes, of course, the 

 jerking and winding motions. Why the impulses traveling for- 

 wards should always reach first the circular, and those traveling 

 backwards first the longitudinal muscles, I have not yet been 

 able to explain. 



These reactions are not peculiar to this special mode of 

 application of the stimulus, but are the consequence of locally 

 applied stimuli. If an earthworm, for example, while crawling, 

 be struck somewhat posterior to its middle point with the dull 

 edge of a scalpel, the part of the worm in front of the offended 

 spot continues to crawl, but at a more rapid gait ; while the part 

 beyond the offended spot at once begins to squirm, at the same 

 time being dragged along by the anterior part. Or, again, if 

 the entire normal worm be irritated at its anterior end, it is 



