DUCTI^SS GLANDS — TAYLOR 711 



tree toad and certain varieties of lizard, particularly the chameleon, 

 apparently change the color of their skins to match the background 

 upon which they lie or cling. Many fish also are endowed with this 

 ability. Even the common frog is of a darker tint in subdued light 

 or on a dark background than it is in bright sunshine, where it 

 appears to become " bleached " to a much lighter shade of green 

 or yellow. 



The frog's skin, as you know, is not of a solid color, but is marked 

 with dark spots or blotches which overlie a light greenish-yellow 

 ground. This mottling is particularly well marked in one species, the 

 leopard frog. If the dark spots are examined beneath the micro- 

 scope, they will be found to be made up of groups of cells with 

 many branching arms and containing granules of a dark pigment. 

 These cells expand in the dark or in dim light and contract in bright 

 light. Or, I should say, rather, that the pigment collects near the 

 center of the cell when the light is bright, but streams throughout 

 the whole cell and into its branching arms when the frog is in dark- 

 ness. So the blotches become larger and take up a greater part of 

 the skin pattern, and less of the underlying green or yellow pigment 

 of the skin shows through. This action of the cells of the frog's 

 skin was a puzzle to biologists for years. They thought that nerves 

 must be concerned in the reaction, yet this could not be demonstrated 

 with general satisfaction. One competent observer, for instance, was 

 convinced that the reactions were carried out through the sense of 

 touch in the skin of the toes, for, he said, when the toes were rendered 

 anesthetic by cocaine the responses did not occur. He thought that 

 the textural qualities, hardness, roughness, etc., of the various ma- 

 terials, such as stone, grass, wood, earth, etc., upon which the animal 

 rested produced color reactions in the pigment cells corresponding to 

 the color of these materials. In other words, the nerves established 

 an association between the texture or any other " touchable " quality 

 of a material and its color. This theory, on the face of it, seemed 

 improbable, and it is not at present entertained. 



If a few tadpoles be taken and their pituitaries removed — this can 

 be done quite easily in this creature, for the gland lies in an accessible 

 position beneath the upper surface of the head — very soon we should 

 find that the animals had lost their natural dark color and appeared 

 as mere silvery ghosts of their former selves. This suggests to us at 

 once that the same thing which bleaches the tadpole also bleaches 

 the frog. Does the lack of pituitary secretion cause the pigment 

 granules to retreat to the center of the cells, and does the presence of 

 the hormone in the blood cause them to spread throughout the cell 

 body? We can easily put this suggestion to the test. If a frog be 

 injected with an extract of the posterior lobe, its skin within a mo- 

 ment or two becomes coal black. After removal of the pituitary, on 



