2 University of California Publications in Zoology [Vol. 27 
inhabit the deserts of southeastern California and southwestern Ari- 
zona (as for example, Bufo punctatus). But all of these species 
require water for spawning purposes. 
In eastern North America and western Europe, where the life- 
histories of amphibians, particularly the Salientia, have been studied 
in detail by numerous observers (see especially Wright, 1914, and 
Boulenger, 1897-98), the accumulated evidence goes to show that 
temperature is the most important factor in the environment. The 
time of emergence from hibernation in the spring and the time of egg 
deposition hinge closely upon the arrival of particular temperatures 
in the air or water or both. Below certain limits, which are different 
for each species, the animals do not leave their winter retreats. Once 
the appropriate minimum is reached their appearance may be expected 
with confidence. The findings of European and American investi- 
gators are in agreement on this point. Some species are evidently 
influenced by other factors in the environment, but these have not yet 
been investigated sufficiently if at all. One point is certain, however : 
the amphibians of eastern North America and western Europe are to 
be found in regions 1 abundantly supplied with moisture through the 
season of their aboveground activity. 
Study of the regulating conditions for amphibians in a semi-arid 
region, particularly one in which extremely low temperatures are 
rarely or never experienced but where the moisture relations are quite 
different, might be expected to reveal interesting adaptive responses 
on the part of the amphibians of the region. It was with this point 
in view that the present study was undertaken. 
Studies on the life-histories of common amphibians, particularly 
the Salientia, involving the entire local fauna, have been carried on 
at Ithaca, New York, by A. H. Wright (1914), at Waco, Texas, by 
J. K. Strecker, Jr. (1908; 1910), and in California by the writer as 
detailed in the present paper. Wright’s studies are by far the most 
complete of any which have been made in any one locality in North 
America, setting a standard toward which other workers in this field 
may well strive. Strecker ’s published data, save for three species, 
relate only to spawning seasons, and while very useful so far as they 
go, leave much still to be learned. They indicate in a general way the 
seasonal program of the amphibians in central Texas. The present 
writer’s results are intended to outline the seasonal programs of the 
various species; the primary effort has been to learn the main points 
in the life-histories of as many species as possible. An endeavor has 
