The Behavior of Cells 183 



behavior. In many crustaceans, fishes, amphibians 

 and reptiles the pigment cells appear at times to 

 be richly provided with branched processes, and 

 at other times nearly all the pigment appears to be 

 concentrated in a rounded mass. These changes 

 often produce marked changes in the color of the 

 animal. They are to a certain extent under the 

 control of the nervous system, but they may also 

 take place independently of nervous influence. The 

 writer has succeeded in isolating pigment cells from 



\ 



Fig. 4. — Successive changes In the form of an isolated pigment 

 cell from a frog. 



various amphibian larvae and also from the adult 

 frog and in keeping them alive In hanging drops of 

 blood plasma where their various changes in form 

 could be followed with the greatest readiness. The 

 pigment cells were seen to undergo changes in form 

 similar to their changes in the skin, putting out 

 processes here, drawing them in there, and in some 

 cases creeping along the cover glass for a consid- 

 erable distance. These cells, like their relatives, the 

 connective tissue cells, have a strong positive thig- 

 motaxis. Loeb found that in the embryos of the fish 

 Fundulus they tend to appear along the course of 



