vations disproved this concept. Nelson reported 

 that C. virginica transplanted from the United 

 States to England could be induced to spawn at 

 19.1° C. (Nelson, 1931). Some of the oysters 

 of Long Island Sound spawn at 16.4° C. (Loosan- 

 off, 1939). 



Ecological evidence shows that spawning of an 

 oyster population often coincides with a rapid rise 

 of temperature but it is not determined by a 

 specific "critical" temperature. Phj'siological 

 studies at the Woods Hole laboratory indicate that 



temperature and chemical stimulation, acting 

 singly or jointly, may induce spawning in sexually 

 ripe oysters. On the other hand it is apparent 

 that certain internal and external conditions in- 

 hibit spawning. 



The effect of temperature on spawning can be 

 observed by placing a sexually mature oyster in a 

 tank of water, connecting its right valve to the 

 writing lever of a kymograph, rapidly warming 

 the water and then maintaining the temperature 

 at a desired level. Shell movements of the 



FiouRE 279. — Transverse section of the gills of female C. virginica preserved during spawning. 



eggs inside the water tube (center) and in the ostium. 



Hematin-eosiu. Note the 



ORGANS OF REPRODUCTION 



307 



