1913] Holmes: Pigment Cells from Larvae of Amphibians 147 



branches. Several times I have watched the formation, meeting 

 and fusion of cell processes, and have seen pigment granules flow 

 freely past the point of union. A large cell may form in this 

 way a considerable network of anastomosing branches. 



The line separating endoplasm and ectoplasm is fairly sharp. 

 The endoplasm, aside from the pigment granules, is not so trans- 

 parent as the ectoplasm. It frequently contains remnants of 

 yolk spherules in the central part of the cell. The pigment is in 

 the form of small round black granules of nearly uniform size. 

 In the narrower processes of the cell the granules are frequently 

 constrained to pass single file, and sometimes a group of them 

 may get wedged together and block the flow, leaving a stretch of 

 the process free from pigment. 



Processes of any considerable size devoid of pigment were 

 not seen. The endoplasm with its pigment granules follows so 

 closely the outpushin'gs of the ectoplastic layer that the forma- 

 tion of a new branch of the cell makes very little headway before 

 it is invaded by pigment. In all the free chromatophores observed 

 the outline of the pigmented area gave a very faithful picture of 

 the outline of the cell. 



The amount of pigment in the chromatophores varied greatly. 

 Some cells were densely crowded with black granules; others 

 contained but very few. In fact every gradation occurred 

 between very dark pigment cells and wandering cells which were 

 probably destined to form connective tissue. Melanin granules 

 occurred also in various other kinds of cells, especially the outer 

 cells of the ectoderm. 



Despite many attempts to obtain free pigment cells there 

 were only a relatively few preparations in which these cells 

 isolated themselves from the surrounding tissue. The melano- 

 phores from older larvae apparently lose some of their power of 

 migration, partly perhaps on account of their greater complexity. 

 As the larvae grow older the branches of the pigment cells 

 become more numerous; anastomoses of the branches are more 

 frequent, and it is doubtless more difficult for the cell, should it 

 retain its power of amoeboid movement, to escape from its con- 

 finement among the other cells. Teasing up the tissue of older 

 larvae in order to facilitate the isolation of the chromatophores 

 gave only negative results. 



