164 
PACIFIC SCIENCE, Vol. II, July, 1948 
A great number of the captive crabs main¬ 
tained in the laboratory were injured specimens 
(individuals which had lost one or more perei- 
opods). The post-exuvial size increment data 
for these individuals were recorded separately 
and compared with the data derived from nor¬ 
mal captive animals. It was found that, in gen¬ 
eral, the magnitude of variation in size incre¬ 
ments of injured crabs is less than that for 
normal captives; in addition, the individual 
post-exuvial size increments are significantly 
less. Underlying factors responsible for this 
phenomenon seem at this time to be largely 
conjectural. MacGinitie (1937) infers that 
mutilation may stimulate molting in Crangon 
californiensis as well as in other macrurous 
forms. There are, however, no data presented 
to support this inference. Several controlled 
experiments on regeneration in P. crassipes indi¬ 
cate that both acceleration and slackening of the 
intermolt cycle may occur, depending upon the 
degree of integumental development at the time 
of mutilation (see p. 194). Mutilation prior 
to stage C 3 lengthens the intermolt interval in 
P. crassipes. Limbs severed during the early C 4 
stage show an accelerated regeneration, but the 
intermolt interval is normal. It would seem 
that an accelerated intermolt cycle would be 
advantageous after the loss of one or more 
appendages because it is certain that maximal 
efficiency in activities concerned with general 
welfare would be dependent upon the entire 
complement of appendages. However, further 
study is required for a satisfactory solution to 
this phase of the problem. 
Comparative studies on the post-exuvial width 
increments of male and female crabs indicate 
that no significant variation between the sexes 
occurs until an initial width of approximately 
25 millimeters is attained. The foregoing in¬ 
formation was secured by plotting initial and 
post-exuvial widths of both sexes from recent 
molts and exuviae collected in the normal 
habitat (Fig. 9). The ratio of initial to final 
width remains approximately identical for both 
sexes until two rather distinct ratios become 
apparent, with the digression taking origin in 
those crabs about 25 millimeters in initial width. 
The smaller post-exuvial size increments of 
females after attainment of sexual maturity show 
why representatives of this sex are invariably 
smaller than males in a given intermolt cycle 
after the tenth to twelfth molt (Table 3), and, 
in addition, show why the largest specimens 
collected are always males (Fig. 9). 
Fig. 9. Sexual dimorphism in post-exuvial width 
increments for P. crassipes. These data are derived 
from measurements of recently molted wild crabs for 
which the exuviae were found. The lines have been 
fitted by eye. 
Exuvial Frequency 
Prior to a consideration of the number of 
exuvial stages during the life span of P. cras¬ 
sipes, it is necessary to point out that reproduc¬ 
tive activity, to a certain extent, alters the usual 
exuvial succession in females. There is evi¬ 
dence to indicate that coition occurs by the 
time the female reaches stage A 2 (see p. 199). 
It has been shown previously in this paper that 
the ova are extruded onto the pleopods during 
stage C 3 , and are subsequently hatched during 
stage C 4 . Approximately 25 days are required 
for an average-sized adult female to reach stage 
C 3 at which time ova would be extruded onto 
the pleopods. About 30 days are required for 
the incubation period, which is concluded 
toward the end of stage C 4 . Some 10 to 15 days 
