260 
University of California Publications in Zoology [Vol. 27 
Maximum discharge in 
second-feet 
1909 January 1 6,150 
1910 March 21 1,780 
1911 January 29 5,910 
1912 March 12 1,080 
1913 January 15 925 
1916 January 17 18,800 
1917 February 21 11,300 
1918 March 12 6,200 
According to the notes accompanying the report for 1913 (the driest 
year in the decade upon which the graph is based) there was, through 
that season, water in pools along the course of the creek even when no 
flow could be recorded by the gage. Such pools would of course serve 
as places of refuge for boylii. It will be noted that the peak of high 
water is, on the average, reached in March. By April first the stream 
is decreasing in volume and only exceptionally does it rise after that 
date (maximum of May 7, 1915). Even in an unusually dry year 
(such as 1913) there is a small flow of water in the stream during the 
spring months and this water lasts until mid- July. 
The temperature of the water in many of these foothill streams 
during earlier months of the year is not unduly low and would not 
be inimical to the eggs of boylii. The adults are easily able to with- 
stand such temperature, as is indicated by their activity in March and 
earlier when the streams are still swift and turbid. But eggs deposited 
during the period of rapid and turbid flow would be likely to be washed 
downstream or else would fail to receive any great quantity of heat 
from the sunlight. Should eggs be deposited and hatch during this 
period of rapid-flowing turbid water, the larvae, especially w T hen in 
the inactive stage immediately following hatching, would be washed 
downstream or killed by being buried in sediment. On the other 
hand, if the larval period should continue into the early autumn 
months there would be great danger that many of the larvae would 
fail to complete their growth and metamorphosis prior to the drying 
up of the stream. There is then but a brief period, from April, when 
the water has become clear and the current slow, until early July or 
August, when the stream begins to dry up, during which boylii can 
deposit its eggs with the likelihood that they will hatch and the larvae 
pass successfully through the metamorphosis. And this is exactly the 
period during which we find the eggs and tadpoles of this frog. 
