Biology of Pachygrapsus crassipes —HIATT 
151 
a parchment-like consistency. The crab can 
elevate the body upon its legs and move 
with considerable agility. Water absorption 
has terminated and the weight is virtually 
constant henceforth. The color of the cara¬ 
pace is similar to A 4 . No food is ingested 
as yet. 
Period B. Duration: 4 to 6 days; 8.0 per cent 
of the total interval. The carapace is somewhat 
rigid, although deformable everywhere save in 
the protogastric area. The meso- and urogastric 
areas, together with the branchial areas, are 
somewhat rigid; the remaining regions, includ¬ 
ing the branchiostegites and sternal areas, remain 
plastic. The appendages are flexible and may be 
bent without breaking. Feeding is resumed by 
the larger crabs on the sixth day following the 
molt. This period is likewise divisible into two 
stages, depending upon the degree of rigidity 
of the chelae: 
Stage B r Duration: IVz to 3 days; 3.0 per 
cent of the total interval. The integument 
of the merus and propodus of the chela is 
relatively supple; it may be depressed with¬ 
out breaking. Most of the animals begin to 
take food during this stage. 
Stage B 2 . Duration: 2Vi to 4 days; 5.0 per 
cent of the total interval. The integument 
of the merus and propodus now resists pres¬ 
sure; if great pressure is applied it will 
break. 
Period C. Duration: 32 to 50 days; 67.0 per 
cent of the total interval. This period, the most 
extensive of the cycle, is initiated when the in- 
tegumental areas become rigid, although some, 
exhibiting less convexity, may retain their plas¬ 
ticity throughout the first two stages of this 
period. Complete sclerotization is achieved by 
the onset of Stage C 3 , making it mandatory that 
other diagnostic criteria for integumentation be 
employed beyond this point. This period con¬ 
tains four stages with a fifth stage a likelihood: 
Stage Q. Duration: AVz to 5 days; 8.0 per 
cent of the total interval. Except for some 
elasticity in the anterior and posterior 
branchial areas together with the concave 
intestinal region, the carapace is completely 
rigid. The branchiostegites and sternites 
are still flexible, as are the carpus and merus 
of the ambulatory legs which may be bent 
in the flattened direction. The broad sides 
of the pereiopods may be squeezed together 
very easily. 
Stage C 2 . Duration: 7 to 10 days; 14.0 per 
cent of the total interval. With the excep¬ 
tion of the intestinal area the carapace is 
entirely rigid. The branchiostegites, ster¬ 
nites, and ambulatory legs are less flexible 
but have not attained rigidity. It is rather 
difficult to distinguish between stages Q 
and Co, inasmuch as these differences are a 
matter of degree. The recognition of each 
stage must be gained through experience. 
Stage C 3 . Duration: IV 2 to 11 days; 15.0 per 
cent of the total interval. At the initiation 
of this stage the entire exoskeleton becomes 
rigid, making it easily distinguishable from 
Stage C 2 , and the internal membranous 
layer has not yet been formed, thereby dif¬ 
ferentiating this stage from Stage C 4 . At 
the termination of Stage C 2 the principal 
layer is completely synthesized, whereas the 
membranous layer becomes totally synthe¬ 
sized at the termination of Stage C 3 . There¬ 
fore, the four integumental strata are com¬ 
plete at the onset of Stage C 4 . 
Stage C 4 . Duration: 15 to 22 days; 30.0 per 
cent of the total interval. This is the most 
extensive stage of the cycle and is primarily 
characterized by the completion of the in¬ 
tegumentary skeleton. The internal mem¬ 
branous layer, when present in its early 
stages of genesis, is not closely adherent to 
the more external principal layer synthe¬ 
sized previously. By cracking a portion of 
the carapace and cautiously elevating it, the 
shiny membranous layer is seen to overlie 
the epidermis. The distinction between 
Stages C 3 and C 4 is perhaps the sharpest be¬ 
tween any two successive stages. For rapid 
diagnosis the following procedure has been 
