MOVEMENTS, ETC., OF FRESH-WATER PEANARIANS. 645 



dividuals capillaries of faster or slower rates than what may 

 be called the standard. After preliminary experiments to 

 determine the relative sensitiveness of the different parts of 

 the body to chemicals, attention was devoted almost entirely 

 to stimulation of the head region, and consequently in tlie 

 experiments which will be reported first the stimulus was 

 applied only to the head, unless otherwise stated. The 

 method of applying the stimulus was to place the ])oint of 

 the capillary tube a short distance (about 2 mm.) from the 

 place on the body to be stimulated. The animal was stimu- 

 lated as it was gliding along in the normal way, and hence 

 it was necessary to move the capillary tube at the same rate 

 the animal moved in order to keep it opposite the same point 

 in case the reaction was not given at the instant the capillary 

 was put into place, which, of course, almost never happens. 

 With a little practice one can move the tube along as the 

 worm glides so as to keep the relative position of the two 

 almost identically the same. Just as soon as a reaction had 

 been obtained with a given specimen the capillary tube was 

 removed from the water, so as to permit as little as possible 

 of the chemical to get into the water surrounding the 

 organism. After a series with any substance, the worms 

 were transferred at once to a dish of fresh water before 

 beginning another series. Further, in any long series, when 

 for any reason it might be supposed that the water was 

 becoming contaminated with the chemical to an extent 

 sufficient to affect the results, the worms were transferred to 

 another dish of fresh water. All through the course of an 

 experiment frequent control tests were made by trying the 

 effect on the worms of the water surrounding thein when 

 diffusing out from the same tube used previously for the 

 chemical. After each experiment the tubes were thoroughly 

 rinsed by drawing distilled water back and forth through 

 them many times. The tubes were also frequently discarded 

 and new ones substituted. 



