Rana tigrina larvae were reared in isolation, at various densities and controlled food and with Bufo melanostictus larvae in laboratory populations. Growth is sigmoid in isolated mdtvtduals and mass reaches a maximum just before metamorphosis. laboratory survival the larval period was independent of initial population but of the population that successfully completed metamorphosis was a negexp'?nenttal density. This is interpreted as the result of the slower growth rate in populatwns ansmg from the competition for food. The individuals in high-density populations wtth slower growth rate take a longer time to reach a threshold size and have a lower probability. of In higher densities, the threshold size for metamorphosis decreases m companson to lower denstty populations.

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4 species of tropical earthworms differed with regard to enzyme activity. The maximum activity of protease and of cellulase occurred in the posterior region of the gut of the earthworms. On the average Octochaetona surensis shows maximum activity and Drawida calebi shows minimum activity for all the enzymes studied.