Biology of Pachygrapsus crassipes —Hi ATT 
153 
D l5 there being no important changes in 
the old integument. However, toward the 
latter portion of this stage gelatinization of 
the membranous layer is initiated. This may 
be easily demonstrated by chipping off a 
segment of the carapace. The broken piece 
will become freed very easily and will re¬ 
veal the gelatinous layer below. Muscular 
insertion on the old integument is not im¬ 
paired since no great diminution in mus¬ 
cular activity is yet apparent. 
Stage D 2 . Duration: 31/2 to 6 days; 8.0 per 
cent of the total interval. This stage is char¬ 
acterized by secretion of part of the pig¬ 
mented layer. Diagnosis is based upon the 
chitinization of the spines, which are hard 
in this stage. When the dactyl is exsheathed 
the new dactyl appears similar to the old 
removed portion, as though the old integu¬ 
ment were a glove covering the new. 
Stage D 3 . Duration: lVi to 314 days; 4.0 per 
cent of the total interval. Resorption has 
now progressed sufficiently far to be recog¬ 
nized. Slight pressure on the epimeral line 
will result in its splitting along its entire 
length. The membranous layer is com¬ 
pletely gelatinous, and resorption is virtu¬ 
ally completed in all parts of the exoskele¬ 
ton. The activity of the crab is much 
reduced. 
Stage D 4 . Duration: 12 to 15 hours; 1.0 per 
cent of the total interval. This abbreviated 
stage immediately precedes exuviation. Re¬ 
sorption is now complete, and the epimeral 
line splits along its entire length. The ac¬ 
tivity of the crab entirely ceases because the 
muscles are now inserted on the supple, 
new integument. The carapace is elevated 
posteriad and exuviation ensues. 
In an effort to test the validity of the identifi¬ 
cation of the various intermolt stages, a com¬ 
parison was made between the intermolt condi¬ 
tion of animals collected in the field and the 
proportional percentage of time represented by 
the individual stages of the entire cycle as ascer¬ 
tained from captive specimens. A field exami¬ 
nation to ascertain the intermolt stage of 574 
individuals was made in 4 days during August, 
1940. Frequencies of crabs within the various 
intermolt stages, together with the proportional 
interval for any given intermolt stages as deter¬ 
mined by laboratory methods, are indicated in 
Figure 2. A marked correlation between field 
and laboratory data is apparent, thus serving to 
confirm in part the criteria for the divisional 
diagnoses of the intermolt cycle set forth above. 
Several phenomena which normally would 
be discussed in other sections of this paper are 
briefly considered at this time because of their 
direct association with various intermolt stages. 
Throughout the examination of the several hun¬ 
dred specimens mentioned in the paragraph 
above, it was noted that ovigerous females con¬ 
stantly fell into stages C 3 and C 4 . The data 
indicate that of a total of 80 ovigerous females, 
23 were classified as stage C 3 , 55 were placed 
FIG. 2. A comparison between the frequency of 
occurrence of the intermolt stages in wild P. crassipes 
examined during August and the proportional extent 
of the individual stages with respect to the time re¬ 
quired for the entire intermolt interval ascertained 
from captive crabs during the same seasonal period. 
The solid line represents the frequency of wild crabs 
in the various intermolt stages; the dashed line indi¬ 
cates the proportional amount of the intermolt interval 
assigned to the various stages. 
