200 
PACIFIC SCIENCE, Vol. II, July, 1948 
ing the mating phenomenon. A hard-shelled 
male was placed in an aquarium with a newly 
molted female and her exuvia. Twenty minutes 
later the male grasped the exuvia with the 
chelipeds and turned over on its back in the 
normal copulatory position. Throughout the 
struggle to arrange the exuvia in the correct 
position, the abdomen of the male oscillated 
rapidly back and forth. This abortive struggle 
persisted for 5 minutes after which the male 
righted itself and moved away. Although the 
male was willing to copulate, a fact deduced 
from its behavior with the exuvia, no attempt 
was made to engage the recently molted female. 
The endopoditic setae of the exuvia above were 
examined and found to contain empty egg cap¬ 
sules (PL 2, Fig. 5), which indicated that the 
non-copulating female described above had been 
ovigerous during the preceding intermolt inter¬ 
val. On another occasion an attempt at copula¬ 
tion was observed between a pair of crabs under 
a ledge high above the adjacent tide pool. The 
animals separated 5 minutes after they were 
discovered. The female was collected and found 
to be ovigerous. The foregoing anomalous be¬ 
havior patterns seem to indicate that the males 
exhibit but slight discrimination toward their 
mating partners. 
Copulation in this species occurs at least 
once yearly and is suspected to take place twice 
annually in some crabs. Recently molted females 
whose exuviae bore empty egg capsules on the 
endopoditic setae invariably exhibited empty 
spermathecae; subsequent impregnation, there¬ 
fore, would be required during the following 
breeding season, or later in the same breeding 
season, providing a second batch of eggs were 
extruded. In many other Brachyura possessing 
far more extended intermolt intervals, it has 
been found that one impregnation suffices for 
the fertilization of the eggs of several egg 
batches which are expelled within a single 
intermolt interval (Williamson, 1903; Churchill, 
1918; Broekhuysen, 1936, 1941). 
Extrusion and Incubation of Ova 
Although the interval between impregnation 
and spawning in P. crassipes has not been ascer¬ 
tained, its direct association with the intermolt 
cycle enables one to estimate the interval with 
considerable accuracy. Inasmuch as eggs are 
never extruded prior to stage C 3 , the interval 
between impregnation and extrusion of eggs 
will depend directly upon the size of the female 
and will vary from approximately 16 days for 
small-sized, mature females to 25 days for large 
females. 
Fertilized ova are expelled from the body of 
the female through the vulvae located on the 
thoracic sternum. They become attached to the 
fine endopoditic setae of the four pairs of pleo- 
pods located on the second to fifth abdominal 
metameres. These pleopodal endopodites are 
clothed for the most part with long, fine setae 
which are simple throughout, with the excep¬ 
tion of a few which branch at the base. With 
the exception of the proximal segment, these 
setae arise in distinct bundles from each endo¬ 
poditic segment (Fig. 18). The tufts arise only 
on the medial, lateral, and posterior surfaces of 
the endopoditic segments; the anterior surface 
is naked. 
The general appearance of the egg mass has 
suggested its usual designation, the "sponge.” 
Eight tufts or clumps of eggs are present, which 
correspond to the eight abdominal endopodites. 
These tufts are so crowded with ova that they 
become contiguous and appear as one mass. The 
sponge of a female measuring 32.0 millimeters 
in breadth is a rounded mass approximately 12 
millimeters long by 40 millimeters wide by 12 
millimeters deep (PL 2, Fig. 3). The eggs 
appear black to the unaided eye, but when 
viewed microscopically with transmitted light 
they are deep brown. The abdomen is forced 
back by the sponge until it describes a 60° 
angle with the sternal surface of the thorax and 
is curved behind the egg mass. A basket-like 
cavity which shields the egg mass is formed by 
plumose setae of the pleopodal exopodites (Fig. 
18) and by the lateral margin of the abdominal 
tergites. 
