ON THE CUTANEOUS PIGMENTARY SYSTEM 
OF) DEE ERG, 
[Philosophical Transactions, Part II for 1858, p. 627. 
Received June 18—Read June 18, 1857.? 
TuHE fact that the skin of the frog is capable of varying in colour, has been 
for some years known to German naturalists. The first account of the 
mechanism by which these changes are effected, appears to have been given 
by Professor Briicke, of Vienna, in 1852,” and the subject has since been very 
carefully investigated by Dr. von Wittich of K6nigsberg,? and Dr. E. Harless 
of Munich.* All these observers describe the dark pigment as contained in 
stellate cells, each composed of a central part or body and several tubular offsets, 
which, subdividing minutely and anastomosing freely with one another and 
also with those of neighbouring cells, constitute a delicate network in the sub- 
stance of the true skin. They describe the dark contents as sometimes con- 
centrated in the bodies of the cells, at other times diffused throughout the 
branching processes, the skin of the creature being pale in the former case 
and dark in the latter. In the tree-frog the change from a dark to a pale state 
of the body generally was induced by bringing the creature into a bright light, 
by psychical excitement (as was supposed *), or by galvanizing the spinal cord ; 
and a similar effect was produced on a particular portion of the surface by 
irritating it mechanically, or with oil of turpentine, or by galvanism applied 
either directly to the part, or through branches of nerves leading to it. After 
the source of irritation was removed, the skin returned somewhat slowly to 
its former colour; and von Wittich noticed that when the paleness produced 
by direct irritation had passed off, the tint became deeper in the irritated spot 
* During the time that has elapsed between the reading of this paper and its publication, several 
new observations have been made, which it has been thought best to introduce into the text, distin- 
guished by date or footnote from the matter of the original manuscript. 
* «Untersuchungen tiber den Farbenwechsel des africanischen Chamaeleons,’ 7v. Band der mathemat.- 
naturwissenschaftl. Classe dev Kaiserl, Acad. d. Wissensch. Wien. This paper I have not yet had an 
opportunity of consulting. 
* Miiller’s Archiv, 1854. 
* Zeitschrift fiiy wissenschaftliche Zoologie, vol. v, 1854. 
° This rests on the authority of von Wittich ; but, for anything stated to the contrary in his paper, 
the effects ascribed to psychical excitement may have been connected with the efforts of the creature in 
struggling, independently of any emotional change. 
