48 
PACIFIC SCIENCE, Vol. IV, January, 1950 
Digestive organ 
Many zooxanthellae occur in the lobes of 
the liver, as is shown in Figure 8. There are 
many grades of disintegration of zooxanthel 
lae. From this fact one may conclude that 
the zooxanthellae are used as food although 
how they pass into the liver from gills ot 
mantle is not clear. 
Fig. 8. Enlarged view of the content of the 
liver. There are many grades of disintegration of 
zooxanthellae in vesicles, probably phagocytic or 
digestive cells. 
Oxygen consumption 
In order to determine whether or not these 
symbiotic zooxanthellae have an effect on the 
physiology of Corculum the oxygen consump- 
tion in the light and in total darkness was 
measured. Two animals weighing about 15 
grams each were placed in glass jars of about 
400 cc. capacity. These were immersed in 
sea water and sealed with stoppers without 
leaving any air bubbles in them. They were 
first kept in total darkness in a simple ther- 
mostat containing sea water. In the second 
experiment they were exposed to the sunshine 
in the same thermostat on the grass land of 
the laboratory. 
Oxygen tensions of the medium were 
measured at the beginning and the end of the 
experiment by Winkler’s method. An injec- 
tion syringe of 5 cc. capacity was used for 
an analyzing vessel. Details of the results are 
given in Table 2. 
There was marked increase of the oxygen 
tension in the light. These increases are cer- 
tainly caused by the photosynthesis carried 
on by the zooxanthellae contained in the gills 
and mantles. The amount of increase is com- 
parable with that shown by reef corals. 
The oxygen consumption while the ani- 
mals were in total darkness is in the usual 
range for mollusks. 
COMPARISON WITH THE TRIDACNIDAE 
It is very interesting to compare these ob- 
servations with the data recorded for Tridacna 
crocea, in which even in the light no signif- 
icant changes in oxygen exchange were ob- 
served (Yonge, loc. cit.) owing, probably, to 
the great bulk of tissues for the amount of 
zooxanthellae present. 
This would indicate that there is no need 
of zooxanthellae for the oxygen requirements 
of the animal. Moreover there is a sufficient 
water current to remove excretory substances. 
One may conclude therefore that zooxanthel- 
lae may be used only for food. 
TABLE 2 
Oxygen Consumption of Corculum in Total Darkness and in Sunlight at 28.5°-31° C. 
CONDITION 
WEIGHT 
DURATION OF _ A 
EXPERIMENT ° 2 INITIAL 
0 2 FINAL 
TOTAL 
DIFFERENCE 
DIFFERENCE 
PER HOUR 
PER GRAM 
gm. 
min. 
cc. 
CC. 
CC. 
CC. 
Dark . 
. 15.8 
70 
4.02 
3.13 
— 0.35 
— 0.019 
Light . . 
. 15.8 
40 
3.90 
4.84 
0.37 
0.035 
Dark . 
. 15.9 
70 
4.02 
3.24 
- 0.32 
— 0.017 
Light . . 
. 15.9 
40 
3.90 
4.94 
0.43 
0.041 
