270 University of California Pvblications in Zoology [Vol. 11 



activity is plotted in an aecompan.ying graph (see fig. 7), some 

 two hundred and sixty-four stimulation periods were necessary 

 to produce the looping response. In the stage of excitement the 

 lation required almost five hours of undivided attention on the 

 part of the experimenter. The animal was not allowed to recu- 

 perate between stimulations, but as soon as it settled to the 

 bottom of the dish and attached itself it was again excited to 

 activity. 



The results given in table VII are the averages derived from 

 six successive stimulations of the series of 264. Thus number 

 one indicates the average duration of swimming period evoked 

 by stimuli one to six ; number two, the average of stimulations 

 six to twelve, etc. This condensation was necessary in order that 

 the curve might be plotted on a convenient scale. Especially 

 in the first individual tested, and to a certain extent in the other 

 two, light stimulation of the posterior end of the animal tended 

 to produce the looping i-esponse. In the stage of excitement the 

 swimming response is readily given to stimulation of the posterior 

 end, but towards the end of the series there is an outcropping 

 of the tendency to move forward by the looping response. This 

 made it necessary in some cases to apply as many as three or 

 four stimulations in order to have the animal move forward by 

 swimming. The number of stimulations necessary at a given 

 period of the experiment is indicated in one of the columns of 

 the table. 



The condition of very indifferent progress is one in which 

 the animal makes slow, jerky, and somewhat incoordinated move- 

 ments very similar to those occurring under the influence of 

 continued action of the various depressants tested on these forms 

 and discussed in a succeeding portion of this paper. The muscles 

 were, however, in a much more rigid state than in the ease of 

 strychnine and chloretone depression ; but also much less tense 

 than was the condition pi-oduced by nicotine. When allowed 

 to remain undisturbed for a few seconds, the animal would eon- 

 tract, and except for an occasional side to side movement would 

 remain in almost absolute quiet. The accompanying graph (see 

 fig. 7), plotted from the data given in Table VII, indicates the 

 degree of activity at the successive periods. The leeches experi- 



