150 
PACIFIC SCIENCE, Vol. II, July, 1948 
.Prior to a consideration of the diagnostic 
characters for each intermolt stage, a brief 
summary of the morphologic pattern of the 
integument is presented, since a knowledge of 
integumentation is necessary in order to imple¬ 
ment definitions of stadia. The integumentary 
pattern was studied and accurately described as 
early as 1860 (Williamson), but we owe our 
present extensive knowledge of its histological 
composition to the work of Vitzou (1882). 
The integumentary strata are described briefly, 
beginning with the outer stratum and progress¬ 
ing inward. The laminar association of these 
strata may be observed in Figure 5. 
1. A thin layer without definite morphologic 
structure (improperly designated cuticle), 
which should be termed epicuticle to be 
consistent with the corresponding forma¬ 
tion in insects (Wigglesworth, 1933). 
2. A series of parallel strata, unequally calci¬ 
fied, occasionally pigmented, which con¬ 
stitutes the pigmented layer. 
3. A series of parallel strata, greatly calcified, 
generally devoid of pigment, thicker than 
the pigmented layer, and providing from 
three-fourths to four-fifths of the entire 
integument. 
4. An internal layer consisting of a very thin 
lamella, which is densely chitinized but 
non-pigmented, and known as the mem¬ 
branous layer. 
It has been known since the work of Vitzou 
(1882) that the epicuticle and pigmented layer 
are secreted by the epithelium before the molt 
and, therefore, underly the old integument; 
whereas, the principal and membranous strata 
are not secreted until after ecdysis. 
The time intervals indicated in the following 
description of intermolt stadia are always the 
result of the function of several integrating 
factors. Important among these are the size 
of the individuals, the temperature of the water, 
and the adequacy of the food supply. The 
writer is acutely aware of the misconceptions 
stemming from data derived from captive ani¬ 
mals; however, the variable factors in the en¬ 
vironment were held to a minimum wherever 
possible. For example, the food supply, which 
in nature is abundant, was completely adequate 
in the laboratory insofar as could be ascer¬ 
tained; the mean daily temperature of the lab¬ 
oratory water varied from 15.2° C. in mid-April 
to 16.3° C. in June. The eight animals employed 
in this study ranged in size from 22.2 to 37.4 
millimeters in carapace breadth. Differences in 
the intermolt interval ranged from 50 days for 
a crab 22.2 millimeters in width to 77 days for 
a crab 34.4 millimeters in width; the mean 
interval was 68 days. The above-mentioned 
intervals are somewhat longer than those oc¬ 
curring in nature for similar sized crabs. For 
this reason, the proportional percentage interval 
of each stage in relation to the entire intermolt 
interval is utilized. Although slight errors may 
occur in case of differential prolongation of 
certain stages in captive animals, the presenta¬ 
tion utilized seems adequate for all practical 
purposes. 
Period A. Duration: 1V^ to 3 days; 4.0 per 
cent of the total interval. This is the period 
which immediately follows the molt. The cara¬ 
pace is completely soft and will depress at the 
slightest pressure of a finger. This period is 
subdivided into two stages: 
Stage A t . Duration: 8 to 12 hours; 1.5 per 
cent of total interval. During these early 
post-molt hours the integument has the 
consistency of a soft membrane. Movement 
is possible, but the animal moves only when 
disturbed and never elevates the body above 
the substrate. The color is brilliant in con¬ 
trast to the pre-molt crab. Water is still 
being absorbed; weight and size are there¬ 
fore indeterminate (Fig. 6). The turgidity 
of the gastric area, due perhaps to the filling 
of the stomach with water during imbibi¬ 
tion, may be felt by passing the finger over 
this area of the carapace. 
Stage A 2 . Duration: 1 to 2 days; 2.5 per cent 
of the total interval. The carapace now has 
