11) Bryant: Horned Lizards of California and Nevada 13 
venience. The skin usually loosens in patches and either falls 
off or is rubbed off. Pieces of skin two inches in diameter were 
found in the cage of some P. b. blainvillei which were molting 
in September. 
Hay (1892) has suggested that the ejection of blood by the 
horned hzard is a protection at the time of molting. This is a 
possibility, but it is certain that the lizard ean just as easily be 
induced to eject blood when it is not molting. Bruner (1907), 
in an interesting discussion, shows the use of the large blood 
sinuses of the head in aiding the molting process. The increased 
blood pressure in the smuses in a measure explains the ejection 
of blood from the eye at such a time. 
Located beneath the horny layer, in the dermis, are numerous 
pigmented cells situated in a layer of cells containing scattered 
yellow pigment granules. These cells constitute the mechanism 
by which the lizard is enabled to change its color. In Phry- 
nosoma, the color change is slow, Coues (1875) stating that the 
change takes place in from twenty-four to forty-eight hours. 
The manner in which the change in color is accomplished is not 
far different from that found in the chameleon and Anolis except 
that the mechanism in the latter instances is more complex. 
Although it is impossible to see the change take place, yet the 
cells involved can be easily studied under the microscope. A 
piece of skin from a juvenile P. b. blainvillei when fixed in 
Erlicki’s fluid and seetioned, showed large round cells filled with 
black pigment situated in the dermis below the scutes. In my 
material the pigmentation was best shown in unstained sections. 
The melanophores possessed many branches leading toward the 
epidermis, each branch dividing and redividing forming a net- 
work. In most instances the branches were filled with the black 
pigment. Between the melanophores and scattered through the 
dermis was a yellowish pigment constituting the ochrophore 
layer. The migration of the pigment outward or inward through 
these branches accounts for a dark or a light color, and is gov- 
erned by the nervous system. Carleton (1903) has shown it to 
be the sympathetic system in the case of Anolis, whereas Briicke 
(1851) and Keller (1895) have shown it to be the cerebro-spinal 
