64 
PACIFIC SCIENCE, Vol. XX, January 1966 
Volume regulation and the normal route of 
water exchange with the environment is via 
mouth and anus. But is the exchange intermit- 
tent or continuous? To test these alternatives, 
1 ml of 0.1% safranine dye was injected through 
the body wall directly into the coelomic fluid. 
The animals were then washed and returned to 
the clear water of their natural environment in 
algal beds on the reef, so that feeding would not 
be interrupted if feeding entailed water circula- 
tion. The colored coelomic fluid could easily be 
seen through the semitransparent skin. During 2 
hr of close observation no apparent coloring of 
water around the animals was detected. Remov- 
ing them from the reef and draining them 
showed that the coelomic fluid still contained 
dye. Animals with coelomic fluid intact when 
placed in tanks containing dye-colored sea water, 
showed no dye uptake after 4 hr of immersion. 
However, the animals were not feeding. 
If water is not circulating by the mouth-anus 
route in a regular fashion, fluids must be "turned 
over" by the animals very slowly. Apparently 
there is no physiological demand for a constant 
flow of water as a carrier for oxygen or food. 
Oxygen could diffuse directly into and across the 
integument where most of the cell population is 
concentrated. This conclusion is supported indi- 
rectly by the fact that these particular holo- 
thurians lack the respiratory trees found in thick- 
walled species (Hyman, 1955). 
While no direct study was made on nutritional 
habits, casual observation indicated an almost 
solid stream of sand mixed with algae being 
waved into the mouth by rhythmic tentacle 
activity. The intestine may be filled solid with 
Environment: 100% sea water 
GROUP 
I 
< 
Fluids taken from animals immediately on removal 
from environment : 
Control 
Coelomic 
V 
Tissue 
Environment^ 80% sea water 
GROUP 
2 
Effect 
of 
dilution 
Fluids taken from animals immediately on removal 
from environment: 
Coelomic 
VI 
Tissue 
0 100 200 300 400 500 600 700 800 900 1000 
r~ — r — r— i — i ___________ i ■ i t — — i — — i 
mOsmols per liter 
Fig. 5. The osmotically active concentrations of coelomic and tissue fluids of animals immersed in 100% 
and 80% sea water for 24 hr. 
