The Rise And Decline Of The Ol\)mpia Oyster 



spring, in the presence of fertilizing substances brought 

 in by the winter rains, account for the high pH at this 

 time. 



5. Market-size oysters bear broods of 250,000 to 300,- 

 000 larvae. The number of larvae per brood depends 

 generally upon the size of the maternal oyster. 



6. Generally each oyster produces one brood per sea- 

 son, but in some years as many as 50 percent bear second 

 broods while in other seasons as few as 75 percent of 

 the individuals spawn as females. Abortions of embryos 

 frequently occur, however. 



7. Spawning of functional females begins in the spring 

 when the minimum, or high tide, temperature reaches 

 12.5 degrees to 13 degrees C. 



8. Most broods of larvae are produced during a period 

 of about 6 weeks at the beginning of the spawning sea- 

 son, though an occasional gravid individual may be 

 found as late as October. 



9. An average period of 10 days is required for de- 

 velopment within the branchial chamber from the time 

 the eggs (diameter, lOOu to 105u) are extruded from the 

 gonad until straight-hinge veliger larvae (length of 

 valves, 180u) are discharged. 



10. As compared with oviparous species, development 

 of the larvae of O. lurida is very slow, and the age of the 

 various stages may be stated approximately as follows: 1 

 day, blastulae; 2 days, gastrulae; 3 days, trochophores; 4 

 days, straight-hinge veliger larvae completely enclosed 

 by valves 110u-120u long; 10 days, veliger larvae with 

 valves 180u-185u long. 



'C3* 



(89) 



