PIGMENT TISSUES 



277 



brown or yellow. Many other animals, as frogs and lizards, change 

 their color in much the same way. 



FIG. 242. An older form of the chromatophore, with two nuclei and well-developed processes, 

 two of which have established connections with nerve fibers, nv.f. (After C. CHUN.) 



Technic. The only special technic to be mentioned in this place 

 is the methods used to 

 depigment the various 

 sorts of pigmented 

 tissue. This process 

 is necessary in order 

 that the structure and 

 relations of the pig- 

 ment cells themselves 

 may be determined. 

 It is sometimes need- 

 less owing to a small 

 amount' of pigment or 

 to a light color and 

 transparency of this 

 material. It is always 

 a supplementary pro- 

 ceeding, and should 

 never be used without 



FIG. 243. Still older chromatophore of a cephalopod. The 

 nuclei are four in number and have become differentiated. 

 The central, pigment-containing region is beginning to appear. 

 (After C. CHUN.) 



a proper relation to the study of the unchanged tissue. When much 

 pigment is present, the tissue should be fixed and hardened first and 



