168 University of California Puhlications in Zoology [Vol. 13 



impossible when the ehromatophore is surrounded l)y other cells. The 

 difference of opinion regarding the movement of chromatophores 

 which this difficulty occasioned has persisted even down to the present 

 time, although the majority of investigators now consider the ex- 

 pansion and concentration of pigment within the ehromatophore as 

 the principal factor in the changes observed. Gaupp (1904), for 

 instance, in his excellent revision of Ecker and Wiedersheim 's 

 Anatomie des Frosches, states : 



Naeh der schon lange von verschiedenen Seiten ausgesprochenen und neuer- 

 dings gut begriindeten Anschauung handelt es sich dabei mir um scheinbare 

 Bestaltveranderimgen, in Wirklichkeit um eine verschiedene Vertheilung der 

 Pigmentkornchen innerhalb der Zellen. Die verastelten Fortsatze der Zellen 

 sind bleibende, constante Theile derselben, in denen jedoch ein Stromen des 

 Farbstoffkornchen stattfinden kann. Es kann also einerseits eine Retraction 

 des Pigmentes aus den Fortsatzen und Concentration desselben im Zellkorper, 

 ja sogar nur in einem centralen Gebiete dasselben, erfolgen: alsdann sind die 

 Fortsatze pigmentfrei, blass und konnen bei der Untersuchung unerkannt 

 bleiben, so dass die Pigmentmasse eine rundliche in sich abgeschlossene Form 

 erhalten muss (Pigmentballung); anderseits konnen die Pigmentkornchen in 

 die feinsten Verzweigungen der Fortsatze ausstromen und dadurch diese her- 

 vortreten lassen: Pigmentexpansion. 



Although my observations on the isolated chromatophores of am- 

 phibian larvae showed that the more prevalent interpretation did not 

 apply to the particular species studied, later investigations of the 

 isolated chromatophores of the adult frog revealed certain conditions 

 more in accord with this interpretation, although showing at the same 

 time its untenability in other respects. 



Pieces of tissue containing pigment cells were cut up in Ringer's 

 solution and mounted in a hollow slide in a hanging drop of lymph. 

 If the lymph coagidated, some of the pigment cells would wander out, 

 either in contact ^\dth the cover slip, or, more frequently, along the 

 free surface of the drop. The observations concerned only the black 

 pigment cells or melanophores of the frog, as the other varieties of 

 chromatophores did not isolate themselves in any of the preparations. 

 The most favorable source was the pigmented peritoneum occurring 

 along some of the veins of the anterior part of the body. The largest 

 melanophores did not wander out, and of the pigment cells that 

 isolated themselves, the smaller ones were, as a rule, the more active. 

 Like epithelial cells, the melanophores showed a marked thignnotaxis, 

 although they did not manifest so strong a tendency to become flattened 

 out as is exhibited by most cells of epithelial origin. 



