BEHAVIOR IN LOWER METAZOA 249 



ments in all directions only those are followed up which bring the ani- 

 mal out of the undesirable situation" {I.e., p. 102). 



In the case of the blowfly larva, Holmes speaks as follows : " Obser- 

 vations which I have made upon the phototaxis of blowfly larvae with 

 the problem of orientation especially in mind soon convinced me that 

 the movements of these forms are directed by hght through following up 

 those random movements which bring them away from the stimulus. 

 When strong light is thrown on a fly larva from in front, the anterior end 

 of the creature is drawn back, turned toward one side, and extended 

 again. Often the head is moved back and forth several times before it 

 is set down. Then it may set the head down when it is turned away from 

 the light and pull the body around. If the head in moving to and fro 

 comes into strong light, it is often retracted and then extended again in 

 some other direction, or it may be swung back without being withdrawn. 

 If a strong Hght is thrown upon a larva from one side, it may swing the 

 head either toward or away from the hght. If the head is swung toward 

 the hght, it may be withdrawn or flexed in the opposite direction, or, 

 more rarely, moved toward the hght still more. If it is turned away from 

 the hght, the larva usually follows up the movement by locomotion. 

 Frequently the larva deviates considerably from the straight path, but 

 as it continually throws the anterior part of the body about and most 

 frequently follows up the movement which brings it away from the stim- 

 ulus, its general direction of locomotion is away from the Hght. In 

 very strong illumination the extension of the anterior part of the body 

 away from the Hght is followed by a retraction, since in whatever direc- 

 tion it may extend it receives a strong stimulus and the larva writhes 

 about helplessly for some time. Sooner or later, however, it follows up 

 the right movement. Occasionally the larva may crawl for some dis- 

 tance directly toward the Hght, but after a time its movements carry it 

 in the opposite direction. When once oriented the direction of locomo- 

 tion of the larvae is comparatively straight " ( I.e., pp. 104-105). 



As Holmes points out, these are only examples of a very general 

 condition of affairs in the lower organisms. We cannot do better, in 

 concluding this brief section, than to quote some of Holmes's general 

 remarks, which show that his observations have led him to essentially 

 the same conception of behavior that we have reached in the present 

 work. 



"The role played by the trial and error method in the behavior of 

 the lower organisms has, as yet, eHcited but Httle comment, owing prob- 

 ably to the fact that attention has been centred more upon other fea- 

 tures of their behavior. It may have been considered by some investi- 

 gators as too obvious for remark, since any one who attentively observes 



