PINEAL GLAND FUNCTION 211 



during expansion and contraction. He explains this migration 

 as a strictly colloidal phenomenon, the contracted and expanded 

 conditions representing respectively the aggregate and disperse 

 phases of a colloidal suspension. This is perhaps the most 

 widely accepted and tenable view. 



Hooker (8) has advanced a third explanation. He believes 

 that the melanophores of frog larvae lie in preformed spaces 

 and that the cells expand and contract as a whole within the 

 spaces which enclose them. The acts of expansion and contrac- 

 tion, according to this theory, are brought about by pseudopodia, 

 the pigment granules being carried in the cell cytoplasm. On 

 this premise the pigment cells are to be considered amoeboid. 



These expansions and contractions are commonly brought 

 about by changes in the intensity of light or heat, but many 

 other agencies will cause a specific reaction. Spaeth (7) has 

 made a detailed study of the reactions produced by a great variety 

 of stimuli upon the melanophores of Fundulus. He notes that 

 the reactions are in every way comparable to those obtained 

 by the same agents upon smooth muscle. He raises the very 

 pertinent question as to whether melanophores may not be 

 considered as modified smooth muscle cells. 



In 1910 Babak (9) noted the reversal of the normal reaction 

 to light when Axolotl larvae were blinded. In diffuse light 

 the melanophores of normal seeing larvae contract. After 

 painting the eyes with an opaque substance the melanophores 

 expand in light. In the same way the melanophores of normal 

 larvae expand in darkness, while those of blinded larvae con- 

 tract. Fuchs (10) explained the phenomenon as due to the 

 intervention of the parietal organ (the pineal gland of higher 

 organisms). He reached this conclusion from a consideration 

 of the phylogeny of this organ. The embryology of the parietal 

 organ in some of the lower reptiles indicates very clearly that 

 this body is a remnant of a third eye. Fuchs assumed that it 

 had retained some of its controlling power over the melanophores. 

 In the normal larvae its influence is completely over-shadowed 

 by the superior power of the functioning eyes. In the blinded 



