1. The ripe ovum of Meretrix meretrix measures 0.06-0.08 mm in diameter, and is covered with gelatinous coating. The spermatozoon bears a cocoon-shaped head, about 0.003 mm in length. 2. On the southern coast of Korea, the spawning occurs from the later part of July, attains its maximum in August and continues to September or October. 3. Only one veliger, 0.19×0.165 mm in size, has been obtained by artificial fertilization, which needed 19 days after fertilization, at 24.3-30.2℃. (room temperature). 4. The author has also tried to identify the full grown veligers by means of tracing back the characteristics of the prodissoconch, on the umbonal portion of the early young shell. 5. The full grown veliger of this species is 0.18×0.16-0.20×0.18 mm in size and much resembles that of Venerupis philippinarum, but it can be distinguished from the latter, by the straight shape of the hinge and the absence of conspicuous teeth on the hinge line. 6. At Kassiri, South Korea, the veligers of this species appear from July to November. 7. Free swimming larval stage continues for about three weeks, then the veliger enters into the completely benthic life as a young shell. 8. The largest young shell the authors has reared up from the veliger larva is 0.50×0.48 mm in size. 9. Conspicuous concentric lines appear along the marginal surface of the young shell during growth. 10. The concentric lines on the shell surface become gradually indistinct, due to the increase of thickness of the shell. 11. In May or June, small shell of 1-3 mm in length are found with the naked eye on the beach. Fishermen believe that these small ones are the spawn of this year. But this idea does not agree with the fact that the spawning season is from July to October and the veligers appear first in July and up to November. 12. By the monthly collection of the small young shells, it was ascertained that the new small shell of the year appears from the later part of July. 13. The shells metamorphosed in the late autumn do not seem to grow till the next spring.