240 HENRY LAURENS 



long continued absence of light, chemical changes in the retinae 

 started impulses which reaching the melanophores caused them 

 to secondarily expand. Briefly, the seat of the causes of the 

 secondary changes were assumed to be in the retinae, for which 

 there was abundant experimental proof, just as Babak assumed 

 that the reactions of the melanophores of the normal larvae 

 were due to the influence of the eyes, which were opposite in 

 effect to direct stimulation of the melanophores themselves. 



Now Fuchs ('14, p. 1545) considers that Babak's explanation 

 of the differences between the reactions of the melanophores of 

 normal and blinded Axolotl larvae is unsatisfactory and seeks 

 to explain it by advancing a theory based on the results of von 

 Frisch's work on the minnow Phoxinus (von Frisch '11, p. 374). 

 As his chief objection to Babak's explanation, he points out that 

 the latter's contention that the expansion of the pigment cell 

 is as much an active process as its contraction, and that there- 

 fore the condition of rest is one of medium pigment contraction, 

 is untenable. For all that is known concerning the distribution 

 of pigment in the chromatophore makes it necessary to regard 

 the expanded condition as that of rest, while a condition of 

 medium contraction must be considered as the result of a tonic 

 condition of excitation, no matter where the tonus arises. 



Fuchs therefore offers the following explanation of Babak's re- 

 sults, seeking in the first place to show why the melanophores of 

 young Axolotl larvae expand in the light. Substances, he says, 

 which are perhaps products of inner secretions, but which at any 

 rate are the results of the ordinary processes of life, arise and 

 cause the melanophores to contract. Now if the young larvae 

 are removed from all possibility of external stimulation, then 

 under the influence of these metabolic products the melanophores 

 contract. This is the reason why the melanophores are con- 

 tracted in darkness. But if a light stimulus, at this time, be 

 allowed to act on the parietal organ, then through the stimulation 

 of this organ an impulse is started which inhibits the endogen- 

 ously produced contraction and the melanophores expand. Grad- 

 ually, as the larvae grow older, the eyes develop and gain an 

 influence (i.e., a pigment motor function) over the pigment cells. 



