Biology of Pachygrapsus crassipes — HlATT 
201 
Fig. 18. Front view of the second abdominal pleo- 
pod of P. crassipes from right side. END., endopodite; 
EX., exopodite; PROT., protopodite. 
The number of eggs extruded at one time 
seems to vary directly with the size of the crab. 
To estimate the number of ova contained in a 
sponge, an ovigerous female 36.5 millimeters 
in carapace breadth was selected. Each of the 
eight endopodites which bore the sponge was 
removed and compared. All contained approxi¬ 
mately the same number of eggs; consequently 
the eggs adherent to one endopodite were 
counted and the sum multiplied by eight, which 
yielded a product of 48,604. Although this 
figure is an estimate, it can be reasonably 
assumed that the sponge of an average-sized 
female will contain approximately 50,000 ova. 
This number is considerably less than that esti¬ 
mated for Callinectes (Smith, 1885; Paulmier, 
1901; Churchill, 1918) and slightly less than 
Williamson’s (1903) estimate for C. pagurus. 
No information concerning this subject for 
crabs of a size comparable to P. crassipes is 
recorded. Inasmuch as the size of ova differs 
but slightly in all the crabs noted above, it 
seems probable that the enormous number of 
eggs which comprise the egg mass of the larger 
Brachyura is correlative with the size of the 
animals. 
Excellent opportunities for critical study on 
the incubation of the ova were presented by 
captive females which expelled their ova in 
aquaria. Observations were made at 3-day inter¬ 
vals throughout the entire incubation period. 
A few eggs were removed from the setae, 
examined grossly, and measured. Inasmuch as 
these data were approximately uniform for four 
females under observation, they were averaged 
and are presented in summary in Table 9. 
The foregoing data show that the incubation 
period was approximately 29 days. Other ovi¬ 
gerous females under observation carried eggs 
from 26 to 31 days. The significance of this 
incubation interval to the intermolt cycle has 
been discussed on page 153. Although a uni¬ 
formity in size of eggs was apparent through¬ 
out development, it was found that when first 
expelled, the ova were misshapen and abnor¬ 
mally lengthened. Immediately after expulsion, 
the eggs actually shortened. It was further evi¬ 
dent that during incubation the ova lengthened 
proportionately more than they broadened. This 
differential growth is undoubtedly a manifesta¬ 
tion of the extensive elongation of the larval 
crab in an anteroposterior direction. 
All of the captive ovigerous females exhibited 
irregular abdominal movements. These move¬ 
ments, which were accomplished by moving the 
abdomen backward and forward in jerky 
arhythmic beats, probably served to aid in main¬ 
taining efficient aeration of all the eggs in the 
mass. The wafting motion separates the eggs 
and thus permits the water to circulate among 
them. It is virtually impossible for water to 
circulate in the densely packed, stationary 
sponge. Ovigerous females in tide pools like¬ 
wise wafted the abdomen, signifying that the 
movement is not merely an adjustment to tepid 
and less-aerated, laboratory sea water. The rate 
and periodicity of this wafting procedure were 
