The processes of embryogenesis, namely differentiation and growth, and also the maintenance of the organism, require energy. Needham (1950) claimed that during development carbohydrate, protein and fat metabolism came into operation in that order. This sequence may differ in some species (Løvtrup, 1959a, b). The importance of —SH groups in the morphogenesis of Planorbis exustus was earlier studied using chloroacetophenone (CAP), an —SH inhibitor, which caused arrest of development, delay in cleavage, exogastrulation etc. when cleavagestage embryos were treated (Mulherkar & Sherbet, 1963). Since —SH reactants are also inhibitors of carbohydrate metabolism, we felt it desirable to find out if carbohydrate metabolism preponderates during the cleavage period and thereby decide whether the action of CAP is to inhibit this metabolism or to interfere with the —SH groups taking part in the formation of the mitotic spindle, regarding which Rapkine put forward the theory of reversible denaturation.

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