148 
PACIFIC SCIENCE, Vol. II, July, 1948 
intermolt condition of crabs utilized for experi¬ 
mental purposes, subdivided the total cycle into 
six stages: (1) "newly molted,” (2) "soft,” 
(3) "paper shell,” (4) "hard,” (5) "pillans,” 
and (6) "about to molt.” Each term describes 
the character of the integument which in turn 
is affected by the amount of water in the tissues 
and haemocoelic spaces and the impregnation 
of the integument with calcareous materials. 
Although this system provides a rapid means 
of grouping crabs, it possesses certain disadvan¬ 
tages. For example, the stage "pillans,” the dura¬ 
tion of which is 3 or 4 days at the maximum in 
P. crassipes, is confused with the latter part of 
the period "hard” and the early part of the 
period "about to molt.” Furthermore, the stage 
"hard” includes several easily distinguishable 
stadia which are of considerable importance in 
the cycle. 
Recently, the solution to the problem of 
securing a near universal method for both inter- 
and intraspecific comparisons during the inter¬ 
molt period was proffered by Drach (1939), 
and it is upon his studies on Maia squinado 
Herbst, Cancer pagurus Linne, and Carcinides 
maenas (Linne) that this study of the intermolt 
cycle of P. crassipes is based. 
Drach sought to establish a series of mor¬ 
phologically determinable "stadia” throughout 
the intermolt cycle in order to construct a stand¬ 
ardized key to the changes which occur. Several 
criteria for the establishment of these stadia 
were selected: (1) each stadium should corre¬ 
spond to a definite internal transformation; (2 ) 
the key characters for the extremes of any 
stadium must be easily recognizable, differing 
considerably from those of the stadium preced¬ 
ing or following; (3) a sufficient number of 
stages should be established so that only a small 
fraction of the animals examined falls into any 
one classification; (4) these stadia must be so 
established that all animals collected may be 
successfully and rapidly classified. This approach 
to the problem seems valid because it considers 
the continuous activity throughout the entire 
intermolt cycle and is directed away from former 
designations which imply stages of both mor¬ 
phologic and physiologic inactivity. The advan¬ 
tages of this system may be briefly summarized: 
(1) it is usable for both wild and captive 
specimens; (2) it is valid for comparison be¬ 
tween different intraspecific age classes; (3) it is 
adapted for comparative interspecific use be¬ 
cause of the high degree of uniformity between 
the higher Crustacea with regard to endysis. 
The present study supplements the informa¬ 
tion contributed by Drach for the cancroid and 
oxyrhynchoid types by extending the knowledge 
of the transformations occurring throughout 
the intermolt cycle to a third cosmopolitan 
group, the grapsoid type. 
The classification presented here for P. cras¬ 
sipes is a modification of that set forth by Drach. 
Throughout the classification of the cycle, ex¬ 
ternal morphological signs have been employed 
where possible, and each has been checked by 
utilizing some character concerned in the genesis 
of the integument. The hardening of the exo¬ 
skeleton is diagnostically accurate, but the major 
portion of the cycle occurs during the time in 
which the exoskeleton is hard; hence, other 
indicative characters must be employed. The 
precocious development of the spines of the 
new integument furnishes the diagnostic char¬ 
acter utilized after the old integument becomes 
totally rigid. To facilitate the interspecific com¬ 
parative aspect, Drach’s method of designating 
the various periods and stages is adhered to. 
The cycle is composed of four major divisions 
designated A, B, C, and D. Each major period 
is subdivided into stages with numerical indices 
corresponding to the order of succession. A 
major period, during which minor but distinct 
transformations occur, frequently will have cor¬ 
respondingly more stage indices than a major 
period during which but few transformations 
occur. For example, A, a very brief period, ex¬ 
hibits two distinct integumental transformations 
designated as stages A 1 and A 2 ; while C, a 
relatively long period, exhibits four major in¬ 
tegumental transformations, C 15 C 2 , C 3 , and C 4 . 
The major periods are equivalent in all species, 
