1914] Holmes: Melanopliores of the Frog 171 



experiments with strong as well as with less intense light yielded the 

 same negative result. It may be that light has some direct effect on 

 the form of isolated melanophores, but its influence, if it has any, is 

 not strong. 



From what has been said, the melanophores of the frog show an 

 evident positive thigmotaxis which is different in its manifestations 

 from the thigmotaxis of eetodermic epithelium and various other kinds 

 of tissue cells. An important element in the extension of the pigment 

 cells as well as other kinds, is, I believe, the adhesiveness of the proto- 

 plasm of the newly formed fine pseudopods. In one instance a pigment 

 cell which had partly crept out of a sheet of extending epithelium 

 had sent out a large process which was apparently attached at its 

 end to the cover slip. While the cell was being observed the sheet of 

 ectoderm contracted carrying the base of the pigment cell away. The 

 tip of the cell remained attached so that the cell became pulled out 

 to several times its previous diameter, when finally it loosed its hold 

 and the cell quickly contracted to nearly its original form. The same 

 adhesiveness is shown in the pseudopods of Amoeba and other rhizo- 

 pods, and probably plays an important role in amoeboid movement in 

 general. 



SUMMARY 



Black pigment cells of tissues from the frog cultivated in lymph or 

 plasma sometimes wander out free from other cells. The pigment 

 cells show a typical amoeboid movement and may creep to a con- 

 siderable distance. 



The smaller melanophores are relatively more active and become 

 isolated more often than the larger ones. 



Processes may be formed that are mostly free from pigment, and 

 pigment may flow back and forth within cell processes so that changes 

 in the distribution of pigment in the chromatophores are partly due 

 to the variation in the distribution of pigment within the cell, and 

 partly due to changes in the outline of the cell itself. 



Heat causes a withdrawal of cell processes. 



Light has very little influence in the movements or state of con- 

 traction of the melanophores. 



Pigment cells show a positive thigmotaxis, the newly formed 

 pseudopods being adhesive to solid bodies. 



