Biology of Pachygrapsus crassipes —Hi ATT 
197 
examination was made of 150 individuals col¬ 
lected at Monterey. These were packed in ice 
for 3 hours, and subsequently preserved in 10 
per cent formalin. The branchiostegites and 
gills were removed; both, plus the epimeral wall, 
were washed with a stream of water; the water 
and contents were centrifuged, and the material 
was searched for parasites exclusive of proto¬ 
zoans. No parasitic species were encountered. 
Only one reference to parasitism on this species 
in California occurs (Baker, 1912), and this 
reference concerned an undescribed parasitic 
isopod located in the branchial cavity. Pearse 
(1931) indicates that Japanese specimens of 
P. crassipes have a high degree of infestation 
with the rhizocephalan, Sacculina. However, 
since P. crassipes does not occur abundantly 
within the more northerly range of Sacculina 
and Peltogaster along the western American 
coast, a low incidence of infection might occur 
in the area of overlapping ranges, but infected 
lined shore crabs have never been found. 
REPRODUCTION 
Sexual Dimorphism and External Genitalia 
Only slight sexual dimorphism occurs in this 
species except for the abdomen, which is tri¬ 
angular in the male and subcircular in mature 
females. Sexual variation of the abdomen be¬ 
comes macroscopically apparent in crabs as 
small as 6 millimeters in carapace breadth. In 
females a progressive abdominal transformation 
ensues from a triangular shape in young crabs 
to the attainment of the subcircular form at 
maturity. 
Extensive sexual differences are noted when 
the abdomens are extended. The first and second 
abdominal appendages of the male are modified 
for use as the intromittent organ; the initial 
pair is the larger and has a tubular form, 
whereas the second pair is considerably smaller 
and is located directly posterior to the tubular 
pair. The second pair functions as plungers or 
pistons working inside the tubular appendages; 
together they accomplish the transfer of the 
spermatophores into the genital apertures of the 
female. To effect the transportation of sper¬ 
matophores from the coxal aperture on the fifth 
pereiopod to the intromittent organ, a sheath 
which arises from the coxa encloses the terminus 
of the vas deferens and extends to the base of 
the first intromittent appendage. This sheath 
functions as a funnel to convey the genital prod¬ 
ucts into the intromittent organ. The flexed 
abdomen covers the coxal opening and sheath. 
When the abdomen of a female is extended, 
the oviducal apertures on the third thoracic 
sternite and four pairs of large abdominal pleo- 
pods are apparent (PL 2, Fig. 6). The copu- 
latory structures of the male are inserted into 
the vulvae during impregnation. Inasmuch as 
the intromittent organs of the male are restrict¬ 
ed to movement in an anteroposterior direction 
and the vulvae of the females are immovable 
(except perhaps for slight stretching in stage 
A x just after ecdysis), it is evident that a suc¬ 
cessful spermatophoric transfer could hardly 
be achieved between crabs differing greatly in 
size. The ova issue through the vulvae and 
become adherent to the endopoditic setae of 
each pleopod, thereby forming the egg mass 
(PI. 2, Fig. 3). 
Age and Size at Sexual Maturity 
The age and size at sexual maturity were 
ascertained by a comparison between the size 
range of the total number of ovigerous females 
collected on the coast of central California, 
together with a microscopic examination of the 
ovaries of 50 selected females whose carapaces 
ranged in width from 10 to 24 millimeters. 
The size range of ovigerous females collected 
during the most important spawning period is 
presented in Table 6. The most diminutive 
ovigerous female examined among wild speci¬ 
mens measured 16.9 millimeters in breadth. 
The records secured from dissections of females 
selected for size during the height of the spawn¬ 
ing season are set forth in Table 7. It is ob¬ 
vious, from the data provided in Tables 6 and 7, 
that sexual maturity in females is achieved when 
the carapace breadth measures approximately 
15 millimeters at about the eleventh or twelfth 
month after hatching. 
