Biology of Pachygrapsus crassipes — IilATT 
183 
water. A more thorough investigation of these 
phenomena is required to classify the differen¬ 
tial responses. 
To test further the influence of the ocean 
on this species, 25 normal crabs and 25 blinded 
crabs were released in groups of 5 from a locus 
in a shallow depression atop a large rock sur¬ 
face which was several feet higher than the 
splash zone. The ocean bordered the rock on 
the outer and lateral sides. The air was vir¬ 
tually calm, and the day was bright and warm. 
The wanderings of the crabs for a period of 10 
minutes were recorded (Figs. 13 and 14). The 
solid lines represent uphill travel, and the dashed 
lines represent downhill travel. The concentric 
areas delimit distances of 3, 6, and 12 feet and 
serve to indicate the distance traveled by the 
crabs. With the exception of the landward side, 
the ocean was approximately equidistant from 
the point of release. 
These data show that one of the patent 
behaviorisms of these crabs is to seek a con¬ 
cealing crevice. The normal crabs immediately 
sought the crevices; five gradually attempted to 
make their way toward the ocean. The slope of 
the rock seemed inconsequential inasmuch as 
the animals did not deviate from the general 
direction of travel. It is significant that none 
of the normal crabs left crevices to travel in a 
direction counter to the ocean. 
The data for blinded crabs compared favor¬ 
ably with those secured for normal ones. In 
Fig. 13. The movements of normal P. crassipes 
within a 10-minute period subsequent to their release 
high on the rocks. (See text for details.) 
Fig. 14. The movements of blinded P. crassipes 
within a 10-minute period subsequent to their release 
high on the rocks. (See text for details.) 
contrast to normal crabs, Figure 14 reveals 
that the blinded ones traveled in all directions 
from the locus. Moreover, they traveled in un¬ 
certain paths, frequently reversing and recross¬ 
ing. Those which located crevices were content 
to remain. Those which walked around to the 
top side of the large crevices wandered about 
aimlessly and failed to locate a refuge. Crabs of 
both groups eventually traveled toward the 
ocean; none ventured away from it. 
The response of this species toward wave 
action is virtually stereotyped. Its behavior 
is not that of extreme fear, such as Schwartz 
and Safir (1915) suggest for Uca, although it 
bears an overt resemblance to such behavior. 
The response varied slightly, depending on 
whether the animals were located in tide pools 
or in rock crevices. Upon the initial indication 
of wave action, crabs in a tide pool curtailed 
their activity to a minimum. As the wave action 
became more intense, the animals concealed 
themselves deep in their crevices, and did not 
emerge until the tide receded. 
Crabs under ledges withdrew at the first splash 
of a wave, moved back as far as possible, and 
wedged themselves in by pressing the carapace 
and appendages against the rock. At no time 
were crabs observed in vulnerable locations as 
the tide approached their refuges. Crabs which 
had climbed up to high, less-protected areas 
