200 
PACIFIC SCIENCE, VoL XXI, April 1967 
1966). In brief, during proecdysis the crabs 
have a tendency to lose weight, which can be 
attributed to a loss of water. Between D 3 and 
D 4 the mean weight gain was about 8%. The 
weight change between D 4 and A 4 was an in- 
significant loss of 1.5%. However, the crabs 
gained 18.8% between A 4 and A 2 . No signi- 
ficant weight alterations were noted between 
A 2 and B 4 , B 4 and B 2 , and B 2 and Q. Between 
stages C 4 and C 2 the weight gain was 4.4%. 
No significant changes were found during the 
remainder of the molt cycle. However, the over- 
all weight gain between two successive inter- 
molt stages was approximately 34%. 
The total water content of the crabs during 
the ecdysis cycle was also followed. During the 
premolt stages, the crabs tend to become de- 
hydrated ; the water lost at D 4 _ 2 and D 3 _ 4 was 
calculated to be 8.1% and 7.7% below the C 4 
water content of 70%. The postmolt water con- 
tent was increased from about 62% (D 3 _ 4 ) to 
77% ( A 1j2 ) and 75% (B 4 _ 2 ), but these water 
content changes were statistically not signi- 
ficantly different from the intermolt value of 
70.3%. 
Water Content of Four Organs and (( Remain- 
der ” Throughout the Molt Cycle 
The amount of water in the various tissues 
of a crustacean during the molt cycle has not 
been previously reported. The water content of 
the carapace, mid-gut gland, gills, muscles, and 
"remainder” in P. vigil is illustrated in Figure 1. 
(The values are the means db S.E.) Analysis of 
variance on the arcsin transformed values illus- 
trated that interaction was present, showing that 
the water content of the tissues did not vary 
uniformly throughout the molt stages. 
The greatest fluctuations in water content 
were found in the carapace during ecdysis. A 
decrease of about 5% was noted during the 
proecdysial stages, but this was not statistically 
significant. The gain in water content between 
D 3 _ 4 and A 4 _ 2 was a significant gain of about 
37%. Although the extracellular fluid volumes 
were not determined, this gain could possibly 
reflect a greater extracellular fluid volume. Dur- 
ing the B 4 _ 2 and C 4 . 2 stages, the water content 
was decreased to 20.54%, which was caused by 
the incorporation of calcium salts. 
The alterations in gill hydration are repre- 
sented as the top curve in Figure 1. During the 
premolt stages, the gills lost 4.57% of their 
water content — a significant decrease. After 
ecdysis the gill water content was increased to 
about 87.64%, which was found to be a sig- 
nificant gain. The hydration at B 4 . 2 was in- 
creased to a significant 89.42%. The per cent 
hydration of the gills during the C x _ 2 period 
was not significantly different from that at the 
C 3 _ 4 duration (90.20%). 
Robertson (i960) has demonstrated that the 
gills of Carcinus maenas were the site of water 
and ion absorption but that the antennal glands 
were the sites for the loss of the water and the 
ions. Because the urine of P . vigil was not sam- 
pled, it is not possible to exclude these glands 
and the gills as the sites of water flux. 
The decrease in water content of the muscles 
during the premolt stages from a value of 85% 
to 7 6% was found to be significant, as was the 
increase to 82% at the A 4 _ 2 periods. The fur- 
ther increases during postecdysis were not sig- 
nificant. 
The same type of pattern is seen to occur in 
the mid-gut gland. The intermolt water content 
was found to be 85.16%. The reduced hydra- 
tion during the premolt stages to about 68% 
was a significant drop. During the A 4 . 2 dura- 
tion, the water content was increased to 78.24%. 
The subsequent changes observed during post- 
molt did not differ significantly. 
Excluding the carapace and the remainder, 
the increase of about 1 1 % in the mid-gut gland 
during ecdysis was the greatest alteration. Rob- 
ertson (I960) reported that in C. maenas the 
water content of the mid-gut gland and its fluid 
increased during the early postmolt stages. This 
was attributed to absorption of water via the 
fore-gut. The results reported here for P. vigil \ 
are consistent with those reported by Robertson 
(I960) and also with the findings of Drach 
(1939) for Mai a squinado and Cancer pa gurus, j 
The fluctuations of the "remainder” during 
the molt cycle are also illustrated in Figure 1. It 
is quite obvious that this portion also lost some j 
water during proecdysis. The intermolt water 
content was calculated to be 68.69%, and post- 
ecdysial values of about 65% were significantly j 
different from the former. After ecdysis the 
water content rose to a significant high of 
83.18%. No statistical difference was found 
