162 
PACIFIC SCIENCE, Vol. II, July, 1948 
Geodetic Survey report for the year 1939. The 
readings are surface temperatures taken at Fort 
Point, San Francisco Bay. The figures correspond 
closely to those published by Sumner et al. 
(1914), and to those taken just outside the 
Golden Gate by the U. S. Weather Bureau 
during the years 1915 to 1924. A marked 
coincidence is noted between the exuvial peri¬ 
odicity and the mean surface temperatures for 
the annual period (Fig. 7). It is significant 
that the apices of thermal and exuvial activity 
fail exactly in line. Ecdysis seems to be per¬ 
ceptibly slowed when the surface temperature 
drops below 14° C., indicating that the physi¬ 
ological processes, presumably those participat¬ 
ing in endysis, are slackened in pace. Supportive 
evidence for this thesis was secured from sev¬ 
eral captive crabs of similar size upon which 
a careful record was kept concerning their 
intermolt development through’ the cooler 
months. The normal intermolt interval for 
crabs of 24 to 30 millimeters in width varies 
from 45 to 60 days during the relatively warm 
midsummer months. However, the captives 
which molted in November and early December 
had only reached either stage C 4 or D 4 more 
than 3 months later. The intermolt records of 
these captive crabs show that endysis is slack¬ 
ened to approximately one-half the pace typi¬ 
cally exhibited during warmer seasons. 
To check the findings described above, the 
exuvial frequency of captive crabs together 
with the temperature fluctuations of the lab¬ 
oratory water were recorded monthly. These 
data are combined with the field data shown 
in Figure 7. 
Fig. 7. A comparison between ocean surface and laboratory water temperature and the annual exuvial 
incidence in wild and captive P. crassipes, respectively. The surface temperature readings represent the monthly 
mean temperatures recorded at Fort Point, San Francisco Bay, 1940. 
