496 journal of Comparative Neurology and Psychology. 



ment of the light caused a reversal in the sense of the response. 

 But will anyone maintain that when a wild animal runs away in 

 alarm from a sudden blaze it manifests a negative phototaxis ? 

 It is with such an action as,this, rather than with the reactions com- 

 monly included under the head of negative phototaxis that the 

 retreat of the fiddlers is more closely related. The flight of the 

 crabs from light has all the characteristics of their flight from mov- 

 ing objects in general. Whenever one enters a room where the 

 crabs are kept or makes a small movement in their vicinity they 

 promptly scuttle away; and they often detect one's presence on a 

 beach for a distance of several rods and make for their holes. 

 These reactions we commonly attribute to fear, whatever physio- 

 logical explanation we may offer for them, and anyone who has 

 observed the fiddlers scurrying away from a moving light can 

 hardly fail to ascribe their behavior to the same cause. 



The point of principal interest in the phototaxis of the fiddler 

 crabs is the relation of their lateral orientation to the theories 

 of tropisms. Can we regard orientation as a direct response in 

 which the animal is involuntarily forced into line, or is it rather to 

 be considered as coming under the pleasure-pain type of behavior, 

 and as therefore related to the voluntary seeking of a certain end 

 which is exhibited in the behavior of higher forms ^ In order 

 to explain the orientation of a highly organized form hke an insect 

 or crustacean in which, in most cases, response to light takes place 

 through the eyes, we may assume that light falling more strongly 

 on one eye sets up impulses which are transmitted more or less 

 directly to the leg musculature. We may assume that the exten- 

 sors of the opposite side are stimulated, or the flexors on the same 

 side, or both, and that in consequence of this distribution of im- 

 pulses the animal moves until its body is in line with the rays. 

 In such a case the movements involved in orientation are the same 

 as those employed in ordinary locomotion only the activity of the 

 legs on one or the other side is accentuated according to the posi- 

 tion of the body in relation to the direction of the rays. 



In the fiddler crab, however, the case is different, and we can- 

 not explain the phenomenon in this way. The legs of the fiddler 

 move in a plane approximately at right angles to the sagittal 

 plane of the body, but they are capable of a certain amount of for- 

 ward and backward motion which may be employed to change 

 the direction of locomotion. The movements involved in orienta- 



