io8 



Herbert Eugene Walter 



As might be expected, Table XXII presents a close parallel to 

 Table XXI. The only difference in the relative values of behav- 

 ior, expressed by the averages of rate and time in these two tables, 

 appears in the case of P. maculata. This species, though first in 

 the scale as regards actual rate of locomotion, is second as regards 

 the time required to leave a unit circle, a condition indicating 

 relatively more v^andering on its part than was shown by any of 

 the other worms. 



TABLE XXII 



The average time in seconds taken in passing from the center to the circumference of a circle 10 

 cm in. diameter in directive light 



The Effects of Fatigue. To obtain an idea of generic and spe- 

 cific differences in the effects of fatigue, two sets of averages have 

 been combined. First the average rate of ten worms of each kind, 

 when subjected to lour successive trials, was first ascertained and 

 the difference between the first and the fourth rate was then ex- 

 pressed as a percentage of increase or decrease in rate, as the 

 case might be. Secondly, the time required to leave a unit circle 

 in twelve successive trials was next recorded and the average 

 percentage of increase or decrease in time of the last four trials, 

 as compared with the first four trials, was computed. By com- 

 bining these two kinds of percentages the relative differences 

 in the effects of fatigue upon the individuals of the various genera 

 and species, are clearly brought out. 



If the results of this computation be compared with the con- 

 clusions reached in another way under the preceding paragraphs 

 on "duration of movement," it will be seen that there is a com- 

 plete agreement in the relative behavior of the different genera 

 and species. That is, the worms most subject to fatigue are the 



