146 The Structure of Protoplasm, 



pressure the scales in KCl assume the punctate form, that is to say, 

 all of the pigment granules are withdrawn from the numerous twig- 

 like branches which radiate out into the surrounding tissues, and 

 are aggregated in the central mass of the cell. As the pressure is 

 increased, however, by steps of 1,000 lbs., invariably there is a 

 greater and greater dispersal of the pigment (see Fig. 8) until at 







1000 LSS / IN' 



iOOO 





4000 6000 7000 



SINGLE MELANOPHORE ; SCALE OF FUNDULUS ISOLATED IN N/10 KCL 



Fig. 8. Suppression of the "contraction" phase of the response of a unicellular 

 chromatophore. 



about 7,000 lbs. the pigment reaches the extremities of the proto- 

 plasmic branches and all of the melanophores have becoine com- 

 pletely stellate. 



The "expansion" of the melanophore appears to reach an equil- 

 ibrium value at each level of pressure, and if the pressure is kept at 

 a certain intensity the melanophores remain expanded to the char- 

 acteristic extent. This steady state is reached in 40-80 seconds after 

 each shift in pressure, and is approximately the same whether a 

 certain level is reached from above, during a step-wise decompres- 

 sion, or whether it is attained from below via step-wise increments 

 of pressure. Furthermore, at a given pressure each cell returns 



