Alligator Lizards 31 
of some functional value to the lizard, it seems probable that 
these unstable habitat conditions would allow for individual 
variation and prevent the evolving of any fixed type. Natural 
selection would perhaps favor first one extreme and then the 
other as local conditions changed. 
segregation of the dark and light phases in response to loca 
conditions such as exist on the Wagner-Applegate divide in the 
Siskiyou Mountains. On the north, or Wagner Creek side, the 
mountains rise from the valley floor slightly below 2000 feet 
altitude to a height of 5000 feet. This north slope is covered 
with a dense growth of Douglas fir, madrone, black oak, and 
yew, which near the crest of the ridge grades into an open 
forest of yellow pine. The yellow pine belt gives way in turn 
to still more open country where mountain mahogany is the 
only tree, growing in low chaparral-like thickets with interven- 
ing open spaces. The higher parts of the south facing slopes 
are dry, rocky and treeless, with scattered clumps of sage. 
Gerrhonotus is rare on the heavily timbered north slope but 
occasionally is found clear to the lower border. All that I have 
seen in this environment were heavily pigmented. Seeing the 
animal in its natural environment the observer is impressed by 
the effectiveness of its pattern in concealing it on the humus- 
filled ground. In the yellow pine belt, the lizards are much more 
abundant, but only an occasional individual is heavily pigmented. 
In most individuals from this habitat the dorsal black spots are 
small and well separated, so that the yellow-brown ground color 
predominates. The lizards are found concentrated in colonies 
about decaying pine logs and stumps. At such spots the ground 
is littered with slabs of loose bark beneath which the lizards 
e 
edges of outcroppings of rock, Individuals observed in 
habitat showed little pigmentation and had an unusually pale 
ground color. They approximated the pale brown shade of the 
Ty grass in which they, were foraging. : 
Such color changes as occur in an individual Gerrhonotus 
are gradual and seemingly are not influenced by its mental state, 
the color of its surroundings, or the temperature. During the ae 
