The nerve distribution, esterase location and the characterisation of esterases has been carried out in two species of the genusProsthodendrium. In both the worms nervous system consists of a pair of cerebral ganglia connected by cerebral commissure. From the ganglia three pairs of nerves run anteriorly and three pairs towards the posterior side. Receptors and fine inter-connections of major nerves have also been studied. The enzyme responsible for hydrolising the substrate 5-bromoindoxyl acetate and acetyl thiocholine iodide is found to be cholinesterase. While studying the location of esterases the significance of the colour developed in various parts of the two species has been discussed.