146 TJniversity of Calif ornia Publications in Zoology [Vol. 11 



that migrated out manifested a remarkable diversity. Some were 

 oval with a few short processes ; some were long and narrow ; 

 some had a few very long and slender processes, and others had 

 many branches. By watching a single chromatophore it was 

 easy to see that it changed in form, in many respects, like an 

 amoeba. Processes were protruded here and drawn in there, so 

 as to produce within a very few minutes marked changes in 

 outline. Figures 4^8 (pi. 5) illu.strate successive changes in form 

 of the same cell that were undergone within a half hour. Figures 

 2 and 3 represent in more detail the same cell at different times. 

 A single nucleus could be seen near the center of each chomato- 

 phore when not too deeply overlaid with granules. 



In the melanophores there is a thin outer layer of protoplasm 

 of excessive transparency, so that it requires careful observation 

 even under the ideal conditions that were afforded, in order to 

 follow its course. It would be quite impossible to detect this 

 material when surrounded by other tissues. Within this outer 

 layer is a more fluid endoplasm which contains the melanin 

 pigment. 



The layer of ectoplasm is not a mere membrane that func- 

 tions passively, but an active layer like the ectoplasm of a 

 common amoeba, which it resembles in its mode of behavior. 

 Where a process of the pigment cell is to be formed, the ecto- 

 plasm becomes thickened, then extends, usually as a narrow 

 strand. Soon the more fluid endoplasm invades the process, as 

 in ordinary amoeboid motion, carrying with it the granules of 

 pigment. Processes may continue to extend in one direction 

 many times the diameter of the cell. Usually they are narrow, 

 but occasionally there may be broader sheets of protoplasm put 

 forth which are at first comparatively free from granules, but 

 they are generally invaded before long with more pigment. In 

 an advancing pseudopod the ectoplasm is thin, except at the 

 tip, and comparatively uniform. When the pseudopod is with- 

 drawn the ectoplasm becomes broader and often more uneven 

 in outline. 



Frequently the branches of the chromatophore may meet and 

 fuse. There is established in such cases a perfectly free com- 

 munication between the endoplasmic contents of the two 



