246 DAVENPORT HOOKER 



more probal)le, by the withdrawal of the processes toward the 

 center of the cavity as well. The volume contained by the 

 cavity is always the same. The cell bodies of the expanded 

 cells are much smaller than those of melanophores in the con- 

 tracted phase and the central cavity appears to have diminished 

 in volume, while the processes of the cell have again opened the 

 lumina of the branches. 



It is from those cells which are not quite completely con- 

 tracted that the jiroof that the cavity is not the fixed cell itself 

 is derived. Such cells (fig. 3, B) show the still uncontracted 

 processes, which stand out clearly from the cavity and in which 

 may be seen the cytoplasm of the cell with a few scattered pig- 

 ment granules in it. It is, therefore, impossible to confuse the 

 cell with its containing space. 



In the extreme phase of expansion, the branches of the ca\ity 

 are completely filled with, the protoplasmic processes of the cell. 

 In consequence of this fact, the expansion pattern assumed by 

 each cell is determined by the shape and distribution of the 

 cavity and is in no way assumed by the cell independent of the 

 cavity. 



DISCUSSION 



Those investigators holding the view that the chromato])hores 

 are fixed and immovable cells in whose cytoplasm the pigment 

 streams back and forth, do not attempt to give any idea of the 

 mechanics of such a process, merely stating that within the cells 

 there are at least two types of cytoplasm, which are sharply 

 differentiated from one another, the more fluid of which carries 

 the pigment, ^^llile the assumption of the presence of two 

 types of cytoplasm seems justified for the larval melanophores, 

 neither type moves independently of the other. The ectoplasm 

 and the endoplasm bear the same relation to one another that 

 they do in amoeba, moving together in the changes in cell form. 

 If the melanophore, or to make it more general, the chromato- 

 phore, were such a cell as is assumed by many investigators, it 

 would certainly be unique in the animal kingdom. The control 



