154 
PACIFIC SCIENCE, Vol. II, July, 1948 
in stage C 4 , while stages D 4 and D 2 each con¬ 
tained one berried crab. It seems apparent, 
therefore, that ova are extruded onto the abdom¬ 
inal endopoditic setae during stage C 3 and are 
normally hatched prior to the attainment of 
stage D 4 . In view of the facts that the incuba¬ 
tion period of the ova has been found to range 
from 25 to 30 days (see p. 201), that the normal 
intermolt interval in female crabs ranging from 
16 to 40 millimeters in carapace breadth varies 
from 23 to 40 days (Table 3), and that stages 
C 3 and C 4 combined comprise approximately 
one-half of the entire intermolt cycle, it is quite 
evident that ovigerous females undergo an 
abnormally prolonged intermolt interval. 
Behavior patterns of P. crassipes are obviously 
dependent to a greater or less extent upon the 
intermolt stage at any given time. It was ob¬ 
served that certain crabs in the communities 
under observation tended to remain secluded 
in crevices throughout the daylight hours. Dur¬ 
ing August, approximately half of the tide- 
pool population remained secluded, never enter¬ 
ing into the active life within the pool or its 
environs. A reasonable explanation of this se¬ 
questering habit is found in Figure 7, wherein 
it is shown that more than 55 per cent of the 
total population of crabs was in a relatively 
soft condition (stages A t - C 2 ). During diurnal 
hours crabs apparently seclude themselves imme¬ 
diately preceding ecdysis and remain concealed 
until stage B 4 is attained. Evidence for this 
inference was secured from the fact that diurnal 
collections of crabs in tide pools has failed 
to include crabs in stages D 4 to A 2 . This con¬ 
cealment during daylight hours is almost cer¬ 
tainly an act of self-preservation. A crab in 
stages D 4 to A 2 is virtually defenseless inasmuch 
as the chelae are supple and the muscular inser¬ 
tions are in a state of reduced efficiency because 
of the flexible integument. 
Nocturnal collections, on the other hand, 
consisted of crabs in all stages of the intermolt 
cycle. The absence of light probably provides 
the animals with increased freedom of move¬ 
ment and safety because the vision of predators 
as well as of the crabs themselves, which are 
cannibalistic on occasions (see p. 179), is con¬ 
siderably reduced. Night, therefore, is the most 
opportune time to make collections of this 
species. A representative sampling of all inter¬ 
molt stages may be made at this time, whereas 
it is virtually impossible to do so during day¬ 
light hours. 
It is the writer’s firm conviction that many 
types of experimental data may be accurately 
secured through the use of comparatively few 
animals if the intermolt cycle is correctly diag¬ 
nosed. Therefore, by extending the knowledge 
of the intermolt cycle to the grapsoid group, a 
framework upon which to base both experi¬ 
mental and natural history data is provided. 
Observations in both the laboratory and field, 
particularly the former, will in most cases be 
inaccurate and misleading if the intermolt stage 
of the animals, which represents a clue to their 
physiological state, is not diagnosed and con¬ 
sidered. 
ECDYSIS AND ASSOCIATED PHENOMENA 
One of the most significant features in the 
life history of the Arthropoda is the act of 
molting, an incident in, and an expression of, 
growth. Nowhere among the Arthropoda is the 
process so striking and abrupt as it is in the 
higher Crustacea. Notwithstanding the volumi¬ 
nous aggregation of literature concerning the 
life histories of crustaceans, few descriptions 
of the actual process of ecdysis exist, and none 
has been published upon the exuviation of 
grapsoid crabs. One of the objectives of the 
present study has been to describe meticulously 
ecdysis in P. crassipes. In addition, considerable 
statistical data pertinent to various aspects of 
the molt and its effect on the crab have been 
accumulated and set forth below. From the 
above-mentioned data, an attempt has been 
made to ascertain the age groups in the exist¬ 
ing crab population, as well as the age-size 
relationship. 
Reaumur (1712, 1719) was the first investi¬ 
gator to describe exuviation of a decapod crus- 
