148 University of California Publications in Zoology [Vol. 11 



A sharply defined beam of light was focused on some of 

 the processes of the melanophores, but no clear evidence could 

 be obtained that the light tended to make the process contract, 

 even with long exposure. Even strong light, w^hen the heat rays 

 were filtered out, had little effect on the cell as a whole. A 

 higher temperature increased the general activity of the cell. 

 A warm needle placed immediately above the tip of a pseudopod 

 would cause the ectoplasm to thicken and the pseudopod to be 

 withdrawn more or less, but no very decided movements of the 

 cell could be evoked by the local application of thermal stimuli. 

 I have tried to direct the migration of the cell, by placing the 

 tip of a heated needle over the pseudopods of one side, but met 

 with no success. While the cells were quite active, and changed 

 their form with considerable facility, they seemed to be lacking 

 in the ability to get away from injurious stimulation. The 

 pseudopods would make but little response even if the heat 

 applied was sufficient to injure the protoplasm. Experiments 

 upon stimulating the pigment cells could not be carried on as 

 extensively as was desired on account of paucity of material. 

 It would be of interest to determine the effect of various chemi- 

 cals on the movements of the celLs, but no work on this subject 

 was attempted. 



A few of the early stages in the development of the j'ellow 

 pigment cells were isolated. One of them is shown in figure 

 10 (pi. 6). This cell contained a small amount of yellow pigment 

 and several yolk granules. It showed a distinct amoeboid move- 

 ment. A few minutes after it was sketched it had assumed the 

 form shown in figure 11 (pi. 6). The attempt was made to stimu- 

 late one end of it by a hot needle applied to the cover slip, but 

 the heat was too great and caused the cell to contract suddenly 

 into an almost spherical form in which it remained (pi. 6, fig. 12). 

 This cell showed a much greater contractility than the melano- 

 phores. Older yellow cells that were observed in small pieces 

 of living tissue contained more abundant pigment : they were 

 often irregularly branched, but the branches were thicker than 

 those of the melanophores: In the larvae of Diemyctylus torosus 

 the yellow cells are large and beautifully branched. The branches 

 are fairly uniform in diameter and end bluntly, and they do not 

 anastomose so freely as do those of the melanophores. 



