2l8 LIGHT AND THE BEHAVIOR OF ORGANISMS 



'* In the fiddler crab, however, the case Is different, and 

 we cannot 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 forward and backward motion which 

 may be employed to change the direction of locomotion. 

 The movements Involved In orientation are different from 

 those employed In ordinary running. They are special 

 movements employed to check deviations from a certain 

 course, a circumstance w^hlch would greatly complicate any 

 attempt to explain orientation as a comparatively direct 

 response. The results of observations on fiddler crabs tend 

 to confirm the conclusion reached In studies made on the 

 phototaxis of Ranatra, namely, that light Is followed much 

 as an animal pursues any other object of Interest, such as 

 prey, or Its mate, and until we can give a physiological 

 explanation of these phenomena we are not, I believe. In a 

 position to give a satisfactory explanation of orientation to 

 the direction of the rays of light." 



A similar Idea regarding reactions to light was expressed 

 by Graber much earlier. He says (1884, p. 248), *' Um ein 

 analoges Beispiel aus einer andern Sinnessphare anzufiihren, 

 so benimmt sich hier [exposed to light differing In color or 

 intensity] die Raupe offenbar ganz ahnllch wie In dem Fall, 

 wenn ihr als Futter einerselts Nesselkraut und andererselts 

 Irgend eine andere Pflanze vorgesetzt wird, Indem sle con- 

 stant das letztere verschmaht und das erstere ergrelft, und 

 in dem Sinne konnen wir also auch ganz gut von einem 

 Farbengeschmacke reden." 



3. Frogs and Toads 



The conclusions of Holmes as far as they refer to orienta- 

 tion In animals with image-forming eyes are strongly sup- 

 ported by the observations of Miss Torelle on the response 

 of the frog to light and by the orienting reactions of the 

 American toad Bufo americanus described below. Miss 



