156 
PACIFIC SCIENCE, Vol. II, July, 1948 
though less pronounced than in some astacuran 
forms (the lobster, Herrick, 1896, and Elm- 
hirst, 1923; and the crayfish, Braun, 1875), is 
distinctive. Like C. punctatus, P. crassipes be¬ 
comes drab, losing the characteristic luster of 
the integument so apparent prior to stage D 3 . 
In addition to the pigmentary deposition in the 
new integument during D 3 and D 4 , the opacity 
is probably also the result of the dissolution of 
the deeper layers of the old integument. A sec¬ 
ond morphological indicator of the impending 
molt is the resorption of the lime salts in cer¬ 
tain areas of the integument; namely, the 
branchiostegites, the sterna, and the basi-ischi- 
opodite and meropodite of the chelae (Fig. 
3, R.). The epimeral lines become desclerotized, 
allowing the upper and lower halves of the 
branchiostegite to be forced apart as a result 
of the increased pressure of the haemocoelic 
fluid. This desclerotization occurs several days 
prior to the molt and may be discovered by 
applying slight pressure on the pleural groove. 
Approximately 3 days before the molt, the 
pressure will result in a precocious schism along 
the groove. A third morphological sign of the 
premolt phase is the friability of the carapace. 
Among specimens collected in the field, many 
had carapaces which cracked as they were 
grasped. Upon examination they were found to 
be in stage D 3 . This significant character was 
utilized by Olmstead and Baumberger (1928) 
as the criterion upon which the stage "pillans” 
was based. Crabs of economic importance are 
aptly designated "peelers” in this stage because 
C., carpus; CO., coxa; D., dactylus; F.P., fracture plane; 
M., merus; P., propodus; R., resorption line. 
the old integument may be picked off to reveal 
the lustrous new integument underneath. 
Fig. 4. A diagrammatic indication of the expansive 
movements occurring during the passive phase of 
ecdysis. Diagram A exhibits the relationship of the 
old and new integuments prior to ecdysis. Diagram B 
shows the relationships at the termination of the pas¬ 
sive phase. AR., arch of branchial chamber; AR'., new 
arch of branchial chamber; BR., gill; CP., old carapace; 
CP'., new carapace; E.L., epimeral line; EP., epimeron; 
EP'., new epimeron; N.I., new integument; PL., pleural 
wall; PL'., new pleural wall; ST., sternal plastron. 
On several crabs, the separation of the notal 
and pleural halves of the branchiostegites oc¬ 
curred a day prior to the active phase of the 
molting act. As the rift between the two halves 
of the branchiostegite widens, the gap between 
the two becomes continuous with the transverse 
lacuna between the posterior edge of the cara¬ 
pace and the first abdominal tergite. The ele¬ 
vated carapace resembles the lid of a box hinged 
at the anterior end of the animal, and under¬ 
neath the old integument may be seen the new, 
somewhat wrinkled one. The expansive move¬ 
ments within the body of a crab undergoing 
ecdysis are diagrammatically indicated in Figure 
4. The arrows indicate vertical and lateral ex¬ 
pansion. The new, underlying integument is 
thin and wrinkled prior to the splitting of the 
epimeral line (Fig. 4 A), after which the old, 
thicker carapace is elevated allowing the new 
integument to stretch to the size to which it 
will eventually harden (Fig. 4 B). 
Late in the passive phase the epimeral split 
extends anteriorly almost to the mouth. Some 
inconsistencies with respect to the origin of the 
