Osmotic Relationships in Opbeodesoma spectabilis— Freeman 
67 
water after 24 hr in dilute sea water, in contrast 
to the controls which lose water over the same 
time interval. Initially, if salt is washed out of 
the tissues by draining, the wet tissue weights 
measured after immersion in different sea water 
concentrations are indicative of how osmotic 
equilibrium may be regained. In the case of the 
controls, the 100% salt water is more concen- 
trated than the washed-out tissue, and water 
moves out from cells. However, when the re- 
stored coeiomic fluid is more dilute, the water 
moves from the coeiomic compartment to the 
tissue cells. 
This indicates that changes in coeiomic fluid 
concentration can exert a sizable effect on what 
goes on in the tissues. This may be better ap- 
preciated by inspecting the data shown in Table 
2. The amount of mobile fluid in the coeiomic 
cavity constitutes an average of 77% of the total 
body weight, while the coeiomic compartment 
itself is nearly 4 times that of the tissues. In 
•addition, the tissue is so arranged that most of 
it is stretched into a thin, membrane-like struc- 
ture encompassing the coeiomic fluid, so that a 
quick, thorough exchange between tissues and 
coeiomic compartments is feasible. 
The comparatively low concentrations found 
for tissue fluid might result from the imposed 
48 -hr starvation period. This possibility was 
evaluated by taking samples directly from ani- 
mals feeding on the reef and comparing the con- 
centrations with those from starved animals, by 
both osmometry and chlorosity titrations. Thus, 
osmotic activity due to salts can be distinguished 
from that due to organic molecules. 
The data in Table 3 show that while feeding 
did not increase the tissue fluid mOsmol con- 
centration, it certainly raised the mOsmol con- 
centration of in situ coeiomic fluid. Coeiomic 
osmotic activity in feeding animals now ap- 
proaches that of sea water but, as the chlorosity 
values for both feeding and starved animals are 
TABLE 3 
Comparison of Concentrations of Coelomic and Tissue Fluids in Feeding and Starved Animals* 
COELOMIC fluid 
| TISSUE FLUID 
animal 
DRAINED 
THRU BODY WALL 
no. 
Chlorosityt 
mOsmols/L 
Chlorosity 
mOsmols/L 
mOsmols/L 
Feeding 
1 
18.5 
868 
15.7 
936 
248 
2 
17.2 
760 
14.0 
808 
274 
3 
17.9 
815 
14.8 
87 6 
257 
Average 
17.8 
811 
14.8 
873 
260 
Starved 
4 
18.8 
848 
13.4 
587 
234 
5 
18.7 
868 
13.8 
664 
268 
6 
18.0 
825 
14.4 
697 
270 
Average 
18.5 
847 
13.8 
649 
257 
* One of two experiments. 
f Chlorosity = grams of chloride per liter. Chlorosity values for tissue fluids could not be obtained due to insufficient 
volumes. 
