198 
PACIFIC SCIENCE, Vol. II, July, 1948 
TABLE 6 
Summary of the Size Frequencies of Ovi- 
GEROUS P . crassipes COLLECTED DURING THE FOUR 
Important Spawning Months. 
MONTH 
: 
NUMBER OF 
FEMALES 
COLLECTED ' 
NUMBER OF 
OVIGEROUS 
FEMALES 
RANGE OF 
WIDTH 
(MM.) 
PERCENTAGE OF 
OVIGEROUS 
FEMALES 
May .......... 
20 
5 
28.5-41.5 
25 
June .. 
151 
61 
18.7-39-2 
40 
July ............ 
362 
112 
17.8-39.7 
31 
August ...... 
626 
144 
16.9-44.0 
23 
Fifty selected male crabs were examined to 
ascertain their size and age at sexual maturity. 
The abdomens of the male crabs were extended, 
after which the genital sheaths about the vas 
deferens were excised and transferred to glass 
slides and examined microscopically for the 
presence of spermatozoa. A summary of the 
information secured is presented in Table 8. A 
comparatively precocious sexual maturity is evi¬ 
dent for males. Adulthood is attained in approxi¬ 
mately 7 months, at which time the crabs meas¬ 
ure about 12 millimeters in breadth. Despite 
this early maturity, the males do not participate 
in reproductive activities until the second year 
unless they were hatched within the first 3 
months of the year. 
Most adult females become ovigerous some¬ 
time between April and September (Table 6). 
However, concrete evidence exists to show that 
berried females infrequently occur during the 
remaining months. Ricketts and Calvin (1939) 
note that berried females may be taken in such 
divergent months as February and June. More¬ 
over, the writer has collected the megalops stage 
of this crab at Monterey during March, which 
indicates that hatching occurred in the latter 
part of January and, inasmuch as incubation 
required at least a month, the female involved 
became ovigerous in the latter part of Decem¬ 
ber. Off-season spawning is not uncommon 
among the decapod Crustacea. Herrick (1909) 
has noted it in the lobster, and Broekhuysen 
(1936, 1941) has found it to be characteristic 
of two other shore crabs, C. maenas and C. 
punctatus. 
Copulation and Impregnation 
Pre-nuptial pairing or exhibitionism is lack¬ 
ing in this species, although the former is preva¬ 
lent among the larger Brachyura (Williamson, 
1903; Hay, 1905; Churchill, 1918). Moreover, 
the actual onset of copulation has been noted 
but once during this study, although several 
captive and wild crabs have been found in coitu 
less than a minute after they had been observed 
TABLE 7 
Record of the Age and Ovarian Development of 50 Selected Females of P . crassipes Col¬ 
lected on June 11, 1941. 
BREADTH 
(MM.) 
NUMBER OF 
CRABS 
AGE* 
(MONTHS) 
EGGS+ 
OVARIAN 
DEVELOPMENT 
20.0-24.0 ... 
4 
14-16 
+ 
eggs large; ovary gravid 
18.0-19.9 ................................ 
4 
13 
+ 
eggs large; ovary gravid 
17.0-17.9 ... 
6 
12 
+ 
eggs medium-sized; 
ovary well-developed 
16.0-16.9 ... 
5 
12 
+ 
eggs medium-sized; 
ovary well-developed 
15.0-15.9 ... 
7 
11 
+ 
5 ovaries developed; 
2 undeveloped 
14.0-14.9 ... 
7 
10 
— 
ovary undeveloped 
13.0-13.9 ................................ 
6 
8-9 
—- 
ovary undeveloped 
12.0-12.9 .... 
5 
7 
—- 
ovary undeveloped 
11.0-11.9 ... 
3 
6 
— 
ovary undeveloped 
10.0-10.9 ... 
3 
5 
— 
ovary undeveloped 
* Ages were determined from Figure 10, page 167. 
t A plus sign (+) indicates that eggs were present; a minus sign (—), that they were absent. 
