T W O FIGURES
Which is the active and which the resting state of melanophores is a question that has been a matter of speculation for over a century.
The majority of workers on this subject have declared in favor of the view that melanophores with concentrated pigment are in an active state and that those with dispersed pigment are at rest (Briicke, 1852; Keller, 1895 ; von Frisch, '12 ; Giersberg, '30, and others). This opinion was reversed by Carlton ( '03) whose work on Anolis led him to conclude that the condition of pigment concentration is that of rest and of dispersion that of activity. Bab6k ( '13)' who worked on amphibians, assumed a third position, namely, that both the dispersed and the concentrated states are active ones and that the resting condition is between these two. That the resting state is intermediate to those of complete concentration or dispersion appears to be implied, if not always so stated, in the writings of Abramowitz ( '36), of Osborn ( '38) and of Wykes ('38).
The opinion of the older workers, that the state of pigment concentration is that of melanophore activity was based upon a comparison of color cells and their nerves with skeletal muscle and its motor innervation as first suggested by Briicke. After it had been shown by Pouchet (1872) that the innervation of vertebrate chromatophores was from autonomic sources and not from the cerebro-spinal system, this comparison was no longer appropriate, for, in accordance with this type of innervation, chromatophores should be compared with smooth muscle fibers and not with skeletal muscle-elements. The propriety of this change was seen in the fact that in the action of chromatophores as in that of smooth muscle, tonus was found to play a very significant role. This more consistent interpretation was adopted by Zoond and Eyre ( '34) , Zoond and Bokenham ( ' 3 5 ) , and by Sand ( '35) who modified in this respect Briicke 's original conception. My own position (Parker, '35 b) was a t variance with all these opinions and came from a sug-137