The biochemistry and histochemistry of Pegosomum egretti have been studied using standard techniques. Phosphatases were analysed colorimetrically; the optimum pH for acid phosphatase activity was 5·0 and for alkaline phosphatase was 10·0. The results were compared with those of other trematodes. Histochemical localization of acid and alkaline phosphatases revealed differences in enzyme activity in various tissues. These differences in the site and pattern of distribution of the two enzymes have been discussed in relation to transport of raw materials and the metabolism of the cell concerned.

The development of phase phenism in L. erysimi involved function related changes in the activity of hydrolytic enzymes. The esterase activity decreased from first to third instar and then increased in the fourth instar and adults. The decrease in the third and the increase from fourth instar up to adults was more in alatae than apterae. The acid phosphatase activity was maximum in second instar. It decreased in the third and then increased again in the fourth instar and adults. The increase was more in alatae than in apterae. The alkaline phosphatase showed a similar trend but was in contrast to acid phosphatase and showed low activity in alatae as compared to apterae.