MELANOPHORES OF RANA 247 



by which such a i)r()('Oss, altei'iiately causing expansion and con- 

 traction of the one type of protoplasm within the other, might 

 go on indefinitely, is by no means clear. 



The views advanced for the movement of jiigment in teleosts 

 by Franz ('08 and '10) and Ballowitz ('13) are, however, of a 

 much more definite character. Both of these necessitate that 

 the pigment granules should show some arrangement which is 

 constant for each cell. Whatever the condition found in the 

 teleosts may be, neither of these views can possibly hold for the 

 frog. Not only is there no definite movement or arrangement 

 of the pigment granules within the cell, but an exactly opposite 

 condition is present. The clear pigmentless area at the center 

 of the cell mentioned and figured by Solger ('89), Zimmermann 

 ('93 b), and Ballowitz ('93 a) from the chromatophores of tele- 

 osts is not visible in the melanophores of the frog under normal 

 conditions. An area lighter, in the living, and darker, in the 

 fixed cells of tadpoles, than its surroundings is very evident, but 

 this appearance is not due to the absence of pigment. On the 

 contrarj^, pigment gi'anules are present in large numbers. Wilson 

 ('06) speaks of the work of these three investigators as proving 

 the presence of an aster within the cell. From evidence obtained 

 in this investigation, however, it appears that there is no rela- 

 tion between the pigment granules and any such structure, as 

 claimed by Solger and Zimmermann. 



The hypothesis of Keeble and Clamble ('05) appears to result 

 from their having overlooked the possibility of the presence of 

 preformed spaces within which the cells may move. This is 

 true for the majority of those who claim that the chromatophore 

 is fixed. They have confused the space with the cell which it 

 contains. The argument offered in favor of the fixed cell idea 

 by Kahn and Lieben ('07), Degner ('12) and Spaeth ('13) is 

 far from conclusi^'e. These authors drew or photographed par- 

 ticular chromatophores in two successive complete expansion 

 phases. That in each case the pictures obtained from the two 

 expanded phases are identical is no proof of the permanency of 

 the processes, for if the cells lie in preformed spaces, the branches 



