1. Monthly samples of Echinocardium cordatum were taken at Port Erin in 1932,1933 and 1934, and at intervals at Fairlie Sands in the Clyde.
2. Growth is continuous throughout the year with the exception of February-March. In their first winter the young urchins attain a length of about 10 mm. at Millport and 15–20 mm. at Port Erin. In their second winter they are about 20 mm. at Millport, and 30–35 mm. at Port Erin.
4. The year 1931 was cold and produced a very small brood of young urchins; 1932 and 1933 were warm years and produced very large broods.
5. The young settle below low water and migrate into the interval zone after an interval of four to twelve months.
6. The gonads of the young urchins mature in their second year. Spawning takes place in June–July–August.
7. The nutritive bodies in the ovaries are shown to be derived from the disintegration of relict ova.
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