IX 



THE SKIN 



189 



remarkable changes in form under certain conditions. When 

 the pigment is most expanded, it is widely spread out into 

 numerous branching processes, giving the whole skin a 

 much darker color; at other times it may be contracted 

 into a small rounded mass. Some investigators (Pouchet, 

 Leydig) have attributed the change in the form of the pig- 

 ment to changes in the shape of chromatophores, which 

 were supposed to send out processes and draw them in 



Fig. 49. — Pigment cells from the frog, in different states of extension, 

 (From Verworn's " General Physiology.") 



again like an Amcjeba. While such movements undoubtedly 

 occur in the pigment cells of many of the lower animals, the 

 majority of investigators consider that the movement of the 

 pigment in the chromatophores of the frog takes place along 

 preformed paths, the outline of the cell remaining approxi- 

 mately constant while the pigment granules flow back and 

 forth within the processes, which are transparent, and hence 



