1. The temperature of 10.0° C. was not high enough to induce normal gametogenic activity in most of the oysters. Even the most advanced individuals of this group showed only slight development of the gonad after exposure to this temperature for 35 days. Apparently this temperature is near the biological zero for this activity.2. Ripening of gonads and spawning of oysters of both sexes were achieved at a temperature as low as 15.8° C.3. Wide individual differences in the extent of gonad development among the individuals constituting the same groups were commonly found.4. In all temperature groups, ranging from 15.0 to 30.0° C., the physiologically ripe gametes were generally formed earlier in the males than in the females.5. At 15.0° C. the most advanced males contained a few ripe spermatozoa on the 10th day. Fertilizable eggs were found on the 20th day and spawning was induced by the 35th day. At 20.0° C. oysters with ripe spermatozoa and fertilizable eggs were found on the fifth day. Spawning was induced...