REACTIONS OF MELANOPHORES OF AMBLYSTOMA 251 



for the larvae of Amblystoma punctatum. It has already 

 been pointed out that Babak's explanation of the reactions of 

 the melanophores of the Axolotl larvae also cannot be applied 

 to those of the melanophores of A. punctatum. 



When one considers the relative anatomical insignificance of 

 the epiphysis in the Urodeles (Studnicka, '05 and Warren, '05) 

 it is hardly surprising that this organ should be found to have no 

 influence upon the melanophores. In the teleosts and particu- 

 larly in the reptiles, the epiphysis reaches a high degree of 

 development with a distinct parietal organ, so that in these 

 animals it is possible that it may have an important function 

 in connection with the reactions of the melanophores (Fuchs, 

 pp. 1442 and 1651, and von Frisch, '11, p. 374). Nevertheless, 

 it cannot be assumed from the results of von Frisch's experiments, 

 — which are the only ones that have been carried out previously 

 to specifically test this point — that even in the minnow Phoxi- 

 nus, the parietal organ is responsible for the inhibiting effect 

 produced by stimulation with light. For he found even after 

 the parietal organ had been extirpated (controlled by micro- 

 scopic sections) that stimulation with light of this region still 

 produced an expansion of the melanophores, while shading it 

 caused the melanophores to contract. Von Frisch further 

 found that when the portion of the roof of the brain which extends 

 from the point of junction of the epiphysis with the brain to the 

 posterior commissure is also removed, that illumination may 

 still sometimes result in an expansion of the melanophores, 

 although sometimes there is no change at all. From these 

 results von Frisch is finally forced to conclude that in the re- 

 gion of the diencephalon there must be light perceiving cells 

 which function as an inhibiting center, and from which nerve 

 fibers run to the deeper portions of the brain which are in 

 this way connected with the pigment motor apparatus so as 

 to bring about this reaction of the melanophores. Perhaps, 

 he thinks, these cells are particularly numerous in the parietal 

 organ, perhaps they are identical with the sense cells and per- 

 haps the connecting nerve fibers constitute the 'Tractus pinealis.' 

 But they are not limited to the parietal organ, else, when it was 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, NO. 2 



