186 
PACIFIC SCIENCE, Vol. II, July, 1948 
is relatively greatest in the youngest crabs. Fur¬ 
ther, the ratio gradually decreases as the size 
of the crab increases, reaching the final and 
lowest value in the largest crabs. 
Despite the fact that the visual perceptive 
surface of the eyes of small crabs is compara¬ 
tively greater than that of larger crabs, we 
cannot conclude that their apparent precocity 
results from better vision. Indeed, the larger 
individuals, which possess considerably flatter 
faceted areas that enable them to direct more 
ommatidia toward an object, are certain to 
perceive objects with greater facility. Undoubt¬ 
edly the precocious development of the eyes 
substantially contributes to the alertness of the 
younger individuals but their bolder habits with 
respect to potential danger, and their ability 
invariably to reach food tossed into a tide pool 
before the larger crabs, probably result from 
nervousness peculiar to young crabs, which are 
merely activated by visual stimuli. It is possible 
that their lack of experience and associated 
inhibitions contribute to their behavior. The 
older crabs seem to proceed with far more 
reserve and caution. 
The comparative agility of young P. crassipes 
and H. nudus or H. oregonensis was well illus¬ 
trated when collections were made by rapidly 
turning over rocks along the shore. The imma¬ 
ture specimens of P. crassipes were easily segre¬ 
gated by turning over small rocks and grasping 
the most rapidly moving crabs which were 
invariably this species. The small, sluggish crabs 
under rocks were generally young H. nudus or 
H. oregonensis . The nimbleness characteristic 
of young P. crassipes is in marked contrast to 
the sluggishness of the other two species. Al¬ 
though the cursorial attainments of these small 
crabs are far less effective than those of true 
land crabs, young P. crassipes are definitely segre¬ 
gated behavioristically from the more phleg¬ 
matic marine forms. 
Intraspecific Territoriality 
Early observations on the general behavior of 
P. crassipes disclosed apparent territorial rela¬ 
tionships among individuals in tide pools. In¬ 
vestigators of fossorial land crabs (Pearse, 
1912; Cowles, 1908) have shown that these 
animals return to their burrows from distant 
points on the beach. The behavior was con¬ 
sidered to represent a homing instinct rather 
than a territorial behavior, although Pearse 
states that fiddler crabs would contest the pres¬ 
ence of any crab at the mouths of their burrows. 
Studies on territorialism among the Crustacea 
in general have been neglected, with the excep¬ 
tion of terrestrial isopods (Allee, 1926, 1938; 
Miller, Ph.D. thesis in the Library of the Uni¬ 
versity of California) and the littoral isopod 
genus Ligia (Miller, op. cit.) which achieve 
some degree of social aggregation. No critical 
investigations of territorial behavior among the 
Brachyura exist; therefore the present study 
was undertaken both to satisfy this need in part, 
and to learn certain behavior patterns required 
for a comprehensive understanding of this 
crab. Inasmuch as data will be presented in 
detail at a later date, it will suffice to give here 
only a brief resume of these findings. 
It was not anticipated that territorialism, if 
present in this species, would be as well defined 
as that found among many vertebrates. The 
proportionately enormous crab population, the 
relatively small habitable area, and the tre¬ 
mendous biotic pressure upon littoral species 
tend to complicate interspecific associations and 
to make these associations obscure and com¬ 
paratively difficult to study. 
It was apparent from a 3-year period of 
extensive observations on this species that true 
territorialism with respect to life-sustaining ac¬ 
tivities as exhibited by many vertebrates does 
not exist. However, the refuges are characteris¬ 
tically defended with brisk determination; each 
crab selects the crevice best suited to it and 
thenceforth defends it from all intruders. The 
success achieved in the defense of an area is 
dependent upon the size and pugnacity of the 
individual. Two of similar size will fight 
viciously for a desirable crevice until the most 
virile of .the pair succeeds, a behavior pattern 
reminiscent of the "peck order” first described 
for birds by Allee (1938). Large crabs appar¬ 
ently defend a small area immediately adjacent 
