286 University of California Publications in Zoology [Vol. 27 
of its range probably occurred in relatively recent geologic time. The 
entire life-cycle is spent along the stream. Spawning occurs late in 
the spring as with the other stream-inhabiting species discussed below, 
and for the same reason. 
j. Hyla regilla. This is the most widely distributed and most 
adaptable of the species here studied. It inhabits a very wide geo- 
graphic range and occurs under widely different conditions of tem- 
perature and humidity, yet is remarkably uniform in its structural 
features. Its coloration is highly modifiable and is usually found to 
match closely that of its immediate environment. Likewise in breed- 
ing activities the species shows greater variability than does any other 
form studied, a range of at least three months in spawning dates 
having been detected in one locality. Small size at transformation 
and small size of the adult are probably factors of importance in 
enabling the species to find suitable shelter in the many different 
habitats which it frequents. 
k. Rana aurora draytonii. This, the largest of the native frogs, 
is highly aquatic and inhabits permanent pools of water. It spawns 
in the middle of the winter rainy period when the ponds are at their 
highest. These ponds seldom freeze, or, if they do, the ice does not 
last for more than a part of a day, so there is little or no danger to 
the species from low temperatures. The larval period is long, four 
or five months, a condition which is made possible by the permanency 
of the ponds inhabited. The egg complement is large. 
l. Rana boylii boylii. [The remarks made here will probably be 
found to apply to Rana boylii muscosa of southern California, but no 
actual data on the life-history of that subspecies are available.] This 
frog inhabits only stream courses in the foothill districts of California. 
The adults are active for a considerable period before spawning, if 
indeed they have any inactive period at all during the winter months. 
Spawning is delayed until the peak load of water in the stream has 
passed, when the water is relatively free of sediment. Embryonic 
and larval development are compressed so as to be completed in the 
brief period between the advent of clear water and the time when 
the creeks become reduced to a series of small pools or else dry up 
completely. The adult is active by day as well as by night, probably 
because its haven of refuge, the creek, is available at all times and 
also because there is less danger of desiccation to an amphibian which 
at all times stays 1 within one jump’ of the water. The adult is of 
