242 HENRY LAURENS 



after the pigment motor function of the eyes has developed, but 

 which in eyeless larvae is still present, and remains so until the 

 larvae reach a certain stage of development when, according to 

 the letter of Fuchs' theory, it would be expected to decrease and 

 finally disappear. 



It should be mentioned, of course, that this theory of Fuchs 

 was put forward to explain the results obtained by Babak con- 

 cerning the reactions of the melanophores of the Axolotl larvae. 

 As has been pointed out, these are different in certain points 

 from those obtained by me with the larvae of A. punctatum and 

 opacum. But the main fact with which Fuchs' explanation is 

 concerned is the same, viz. that in larvae deprived of their eyes 

 the melanophores expand when the larvae are illuminated. 

 If his explanation, that this is so because of the stimulation of 

 the parietal organ, by virtue of the fact that impulses going out 

 from it inhibit an endogenously produced contraction of the 

 melanophores, holds for larvae of the Axolotl, it must hold also 

 for larvae of A. punctatum and opacum. The same applies to his 

 belief that when the eyes are present their stimulation starts 

 impulses which are opposite in effect to those sent out by the 

 parietal organ and stronger, so that these are rendered of no 

 avail. 



To test this hypothesis of Fuchs several methods of experi- 

 mentation were employed and these will be taken up in order. 

 But before proceeding to describe and discuss their results it 

 seems desirable that some idea be had concsrning the develop- 

 ment of the so-called parietal organ, and its position at this time 

 and later. To do this it is hardly necessary to more than call 

 attention to the accompanying figures. In figure 1, which is a 

 view of the extreme anterior portion of a sagittal section of a 

 5.3 mm. larva of A. punctatum there is seen the beginnings of the 

 development of the epiphysis and paraphysis. In figure 2, of a 

 6.6 mm. larva, development has proceeded only a little further. 

 In figure 3, which is of an 8.0 mm. larva, the epiphysis and para- 

 physis are both seen as evaginations, the former of the dienceph- 

 alic wall, the latter of the telencephalic, the two cavities of the 

 brain being partially divided by the velum transversum. In 



