368 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



their reactions to light ; consequently a large series of experiments was 

 made to determine their reactions to the two lights of different area. 



The larvae were placed, one at a time, upon the ground-glass plate 

 used in the previous experiments, which, as in the case of Bipalium, 

 was supported about 1 cm. above the table by means of small wooden 

 feet. As with Bipalium, too, the records were taken when the larva 

 reached the first, or inner, circle, so that it crawled a distance of only 

 about 5 cm. In the earlier experiments the glass plate was kept 

 moist in the belief that the moisture caused the larva to keep up its 

 crawling motion ; but later the plate was used dry without essential 

 difference in the results. The animals usually started promptly and 

 crawled rather rapidly and uniformly, as soon as placed on the plate, 

 but in some instances they showed considerable hesitancy and made 

 trials in various directions before going ahead. 



They appear to have three characteristic modes of progression : (1) 

 The most usual manner is by means of the legs alone, the posterior 

 portion of the body being dragged along passively. This part may be 

 held straight, but sometimes it is slightly curved to one side, in which 

 case it is possible that its position influences to some extent the direc- 

 tion in which the animal turns. (2) The larva occasionally crawls by 

 alternate elongation and contraction of the body (made possible by the 

 telescoping movements of the segments), much as an earthworm crawls, 

 and at such times the anterior end is often raised into the air and 

 waved about more or less. (.3) The larva may also move backward 

 for a short distance at about the same rate that it normally crawls for- 

 ward. It seldom goes backward more than two or three centimeters, 

 and then starts forward again, apparently alivai/s turning in one direction 

 or the other, and not going forward in the same line in which it was 

 moving backward. This last reminds one somewhat of the motor reac- 

 tion described for Protozoa and some other animals by Jennings ; but 

 whether it is used for the same purpose in response to strong stimula- 

 tion or other conditions does not concern us here, since it is not the 

 usual method of orientation to light of moderate intensity. 



In the experiments with light falling upon one side only, the larvae 

 were given five trials headed in one direction, and then five headed in 

 the opposite direction ; but in the trials with both lights at once they 

 were headed alternately in the two directions, — one trial in one direc- 

 tion and the next in the opposite. Since in both cases there are the 

 same number of trials in each direction, it is not probable that this 

 difference of method affects the results. Only 50 trials each were 

 made with the two lights separately, whereas 200 trials were made 

 with both operating at the same time. The same five individuals were 



