306 journal of Comparative Neurology and Psychology. 



and the needle is held in place, the animal approaches the needle 

 and tries to capture it without paying the slightest attention to the 

 meat lying directly below. If, after the meat has fallen, the needle 

 is withdrawn and touched to the surface of the water behind or at 

 one side of Necturus, it turns instantly in the direction of the needle 

 not because it sees, but because it feels wave motions coming from 

 that direction. Long experience with Necturus, and with many of 

 its nearer allies, enables me to speak very positively on this point. 

 When it is remembered that in the higher animals the direction of 

 sound waves is given by the auditory sense organs, which are pri- 

 marily surface sensillae homologous with those in the skin of Nec- 

 turus, it may not seem so strange that the animal directs its move- 

 ments in the way described. Necturus can see, but it can feel 

 (perhaps we should say hear) so much more efficiently that its 

 small eyes seem almost superfluous." 



All the facts thus recorded seem to show that the eyes of the 

 young Necturus, as well as those of many other Urodeles, are not 

 highly functional structures, and that when the animal is deprived 

 of their use the dermatopteric sense adequately compensates for 

 the loss. 



As Parker ('05, p. 418) has well said, "The ability of the spinal 

 nerve terminals to be stimulated by light may now be said to be 

 established for certain fishes, amphibians and reptiles; and this 

 fact is not without interest in connection with the theories of the 

 origin of the vertebrate retina." 



The many attempts to explain the inverted position of the verte- 

 brate retina early led to hypotheses by Lankester ('80), Balfour 

 ('85) and Beard ('88) that the eyes are structures which have been 

 evolved from hght perceiving organs which were at one time located 

 in the unclosed neural plate. Bischoff, Kolliker, His, van 

 Beneden and others long since observed in mammals a very 

 early appearance of the optic vesicles. Heape ('84) observed the 

 optic vesicles in the mole when the neural folds were widely open 

 in the head region. Keibel ('89) later observed that in the guinea 

 pig a like early differentiation of the optic vesicles occurs. Whit- 

 man ('89) discovered that in Necturus there is a very early appear- 

 ance of the eye, "its basis being discernible as a circular area long 

 before the closure of the neural folds of the brain." 



No one, however, had ever shown that the optic vesicles were 

 present in the neural plate at the time the neural folds first appear, 



