250 University of California Publications in Zoology [Vol. 27 
Life-history. — Rana boylii boylii is strictly a stream-inhabiting 
frog. The whole life of an individual is passed along a stream, and 
the seasonal life-cycle is closely correlated with the annual cycle 
of the stream. The adult frogs of this species spend much of their 
time perched on rocks in the stream or on the bank, but in the latter 
place they never go more than two or three feet from the margin 
of the water. If approached, even from the direction of the stream, 
they invariably seek safety by leaping into the water, and immediately 
swim with swift strokes down to the bottom. In streams with silt on 
the bottom they hide in the mud and silt which their movements stir 
up ; in clear waters they take refuge under overhanging rocks. The 
obscure pattern of markings on the back and sides of this frog and 
the roughened surface of the skin blend well with most of the back- 
grounds against which the animals are apt to be seen, either above or 
below the surface of the water, and this constitutes a factor of safety, 
at least so far as human eyes are concerned. 
It seems doubtful if Rana boylii boylii has any period of real 
hibernation such as is annually experienced by the frogs in the north- 
eastern states. The winter season in the foothill districts of California 
is very mild. There are very few days upon which the temperature 
drops below 32° F. Only exceptionally does the ground freeze and 
then only for short periods and the depth tO' which the freezing pene- 
trates is but slight. The creeks are never frozen, save occasionally at 
the surface. The mean minimum monthly temperature (text fig. B) 
in the range of Rana boylii boylii does not drop below 36° F. There is 
consequently no need for a hibernating period. The only actual fact 
which bears in any way on the point is the finding of two specimens 
of this species beneath rocks in the creek bed of Claremont (Tele- 
graph) Canon near Berkeley on November 17, 1912. These two frogs 
were not torpid. Evidence from the winter activity of other local 
species of amphibians suggests that there is no need for hibernation 
on the part of this species. Furthermore, the conditions which obtain 
along many of the streams inhabited by Rana boylii boylii are, during 
the winter months, such as would be distinctly adverse to hibernation 
by a stream-inhabiting amphibian. The courses of many of the Cali- 
fornia foothill streams are rocky, with but little mud in the stream 
bed. The winter and early spring time, from November until March, 
when frogs in the east are in hibernation, is, in California, ordinarily 
a period when the streams are swollen with rain water and actively 
engaged, by reason of their increased rate of flow, in the transport of 
