Eycleshymer, Reactions of Necturus. 305 



difference of opinion. The earlier observations of Graber 

 ('84, p. 121) seemed to show that Rana esculenta is negatively 

 phototropic and Loeb considered this probable. Plateau ('89, p. 

 82), however, found that R. temporaria is positively phototropic. 

 Parker ('03, p. 30) also found that R. pipens is positively photo- 

 tropic, not only in the normal condition, but also when the eyes are 

 removed. Later Miss Torelle ('03, p. 487) discovered that 

 Rana virescens and R. clamata are positively phototactic at ordin- 

 ary temperatures, but that raising the temperature to 30° C. accele- 

 rates the rate of positive response, while a lowering of the tempera- 

 ture to 10° C. produces movements away from the light. Koranyi 

 ('93, p. 6) says that microscopical changes in the retina of Rana 

 may be effected by the exposure of the skin, as well as the eye 

 itself, to light. 



The results of experiments on Urodeles seem to be more uni- 

 form than those of experiments on the Anura. Configliachi 

 and RuscoNi were probably the first to point out that some of the 

 Urodeles are negatively phototropic. They noted that Proteus 

 always retreats towards darkness. These investigators thought 

 the effect upon the skin, rather than upon the eyes, caused the 

 animals to seek darkness. Grader's ('84, p. 96) experiments on 

 the young of Triton, in which he found them negatively photo- 

 tropic, even when their eyes had been removed and their heads 

 covered with black wax, led to the assumption that the skin can be 

 stimulated by light. Dubois ('90, p. 356) who covered the eyes 

 with gelatine and lampblack, concludes that Proteus distinguishes 

 light from obscurity both by the eyes and skin, but that the der- 

 matopteric sensibility is far less powerful than the ocular sensi- 

 bility. Whitman ('98, p. 302) says of the young Necturus: "It 

 is interesting to see how little the eyes are depended upon in 

 finding a piece of meat. A bit dropped in front of a young Nec- 

 turus receives no attention after it reaches the bottom. An object 

 must be in motion in order to excite attention, and it is not generally 

 the moving form that is directly perceived, but the movements of 

 the water, traveling from the object to the sensory hairs, are felt, 

 and in such a way as to give the direction of the disturbing center 

 with most surprising accuracy. If a bit of beef is taken up adher- 

 ing to the point of a needle and held in the water, the vibrations 

 imparted to the needle by the most steady hand will be sufficient 

 to give the animal the direction. If the meat falls to the bottom. 



