1,Cockle samples were taken on a flat and in a gully, once a month, from February until June 1968.2. Fixation on formalin does not influence the dry weight, but it does influence the wet weight when compared with boiled cockles: formalin cockles proved to be 1,8x heavier than boiled ones.3, Shell growth: until the 3rd year the percentual increase in length is greater than its thickness. In older cockles the rates are about the same.4, Shell weight per length group decreased in March, but this was already compensated in April.5, Flesh weight (excl. Gonads) decreased until the beginning of April and then an increase was found, the rate of which was highest in May.6, Flesh weight (incl. Gonads) increased already from the beginning of March: the increase of the gonads overcompensated the loss of tissue weight.7, Ovaria: from the beginning of February some showed ripe ova. In the beginning of May all ovaria were ripe and did not show oogonia any larger.8, Testes and ripe sperma from March. In the beginning of May testes weight was highest, but besides of spermia also spermatogonia were still to be seen.9, Eggs and sperm shed from the end of April or the beginning of May (at a temperature of appr. 10°C).10, The cockles from the flat and the gully didn't show much difference. On the flat, the shells were a little bit heavier and the flesh weight was somewhat lower than in the submerged cockles.