562 EAYMOND PEARL. 



given a specific name. I would propose for this reaction the 

 term gouiotaxis.^ 



When a flat-worm starts from a resting condition tlie 

 nature of the movement, i. e. whether gliding or crawling, 

 depends in large measure on the intensity of the stimulus 

 which starts it. If the resting animal is rather strongly 

 stimulated it will start at once into a crawling movement, 

 which changes to gliding after three or four, or fewer, con- 

 tractions, ])rovided the stimulus is not again renewed. It is 

 possible by the use of a very weak stimulus to start the 

 resting animal off at once into the gliding movement, or with 

 only the faintest indication of a single crawling contraction. 

 When the animal starts spontaneously into movement it 

 usually begins at oace with the glide. When starting spon- 

 taneously the glide is usually preceded by some of the 

 " feeling " movements of the head end, such as precede the 

 coming to rest. The purpose of these is evidently the same 

 as in the former case. Any sort of strong stimulus will start 

 the resting animal into movement. 



The physiological condition of the resting animal is, as has 

 already been mentioned, one of relaxation. All of the 

 muscuUir systems of the body are in an apparently com- 

 pletely relaxed condition. This is evidenced by the form of 

 the resting animal, which differs from that of one in move- 

 ment, in being shorter, wider, and thicker, and in not showing 

 such features as the auricles, or the pointed tip of the head. 

 This relaxed condition is evidently one of lowered tonus, as 

 may be determined by simple observation. Stimuli of an 

 intensity which would cause a marked reaction in an in- 

 dividual in an active condition, will produce no effect on a 

 resting animal. This point has been tested with a variety of 

 stimuli, including- mechanical, chemical, food, etc., and the 

 markedly loAver tonus of the resting animal is very evident. 

 The reactions which are produced, provided the stimulus is 

 made strong enough to be just effective, are weak. Of 

 course, if the stimulus is above a certain strength, or is con- 



' From ywri'a = angle. 



