Biology of Pachygrapsus crassipes— Hiatt 
193 
The earliest indication of podomeric differen- 
tation was manifest when the papilla reached 
approximately 1 millimeter in length. Three de¬ 
pressions appeared at this time: two longitu¬ 
dinal, one on each side; and one horizontal, 
immediately below the apex. The longitudinal 
furrow marks the separation of the merus on 
one side and the carpus and propodus on the 
other; the horizontal depression denotes the 
articular area which separates the carpus from 
the propodus. The dactylus became visible a 
few days later, appearing as another longitu¬ 
dinal furrow at the base of the papilla on the 
side containing the propodus. These depres¬ 
sions deepened, and another near the base of 
the merus indicated the division between this 
podomere and the basi-ischium. Regeneration 
in the chelipeds was slightly different from that 
in the ambulatory appendages. The papilla of 
the former was larger and capitate. Only two 
longitudinal furrows were conspicuous laterally, 
and the furrow which marks the separation of 
the dactyl from the propodus differed from 
that found in the ambulatory legs. The dactyl 
of the cheliped is in apposition to the extended 
finger of the propodus, therefore the furrow is 
single, longitudinal, and perpendicular to the 
furrows which indicate the junction of the 
merus and propodus. The remaining podomeres 
developed similarly to those of an ambulatory 
appendage. 
External differentiation of the podomeres was 
complete in approximately 18 to 21 days from 
time of severance, by which time the animal 
reached the C 2 stage. Crab No. 10 attained 
this stage in 13 days. The precocious develop¬ 
ment of the papilla of crab No. 10 is signifi- 
cent because autotomy occurred in early C 4 , and 
complete regeneration ensued prior to the first 
post-autotomal molt. Of the five C 4 crabs from 
which limbs were removed, only crab No. 10 
accomplished complete regeneration by the 
first molt. 
Pigmentary deposition in the podomeres 
took place in the sequence of podomeric differ¬ 
entiation; it began on the merus and propodus, 
later progressed to the carpus and dactylus, and 
reached the basi-ischium last. Pigment was 
apparent about 24 to 27 days after severance 
of the appendage; crab No. 10 exhibited pig¬ 
mentation as early as the sixteenth day. At the 
onset of pigmentation the papillae varied from 
1.5 to 2.0 millimeters in length. 
Appendages severed during stage A 1 required 
between 30 and 33 days to develop papillae 4 
millimeters in length; crab No. 10 reached this 
stage in 18 days. At this time, the crabs which 
underwent ecdysis before papillary development 
had reached stage C 3 or early C 4 . 
Upon the attainment of stage D 4 the papillae 
which exhibited complete podomeric differen¬ 
tiation reached a length of about 7 millimeters. 
Of four completely developed pereiopodal pa¬ 
pillae, three measured 7.1 millimeters and one 
measured 7.2 millimeters immediately prior to 
ecdysis. During the investigation two crabs 
had papillae which grew in an anomalous man¬ 
ner. Both these papillae were severed at ecdysis 
and new, normal papillae were later observed. 
It is evident, therefore, that normal regenerative 
processes may be modified. However, the ab¬ 
sence of malformed appendages in wild crabs, 
combined with the exuvial autotomy of anoma¬ 
lous papillae, suggests that aberrantly formed 
limbs rarely, if ever, succeed in reaching a func¬ 
tional condition. 
The present study on captive animals, in 
addition to extensive collection of wild crabs 
with regenerating limbs, has shown that two or 
more severed limbs will attain the same degree 
of regeneration before ecdysis regardless of when 
autotomy occurred before stage C 4 . However, 
the data at hand are insufficient to ascertain 
whether or not regeneration is accelerated when 
mutilation occurs in an intermolt stage prior 
to C 4 . One would surmise that acceleration 
was inevitable, and the information available 
strongly suggests this phenomenon. 
To obtain information concerning regenera- 
tional development and the intermolt cycle of 
wild crabs, 203 crabs were collected and exam¬ 
ined during March, 4941. Of this number, 58 
had nearly mature papillae (i.e., papillae with 
