Using the indigogenic technique for localizing the non-specific esterases, the complete nerve arrangement inFischoederius elongatus andGastrothylax crumenifer, the paramphistome parasites in the rumen of cattle, has been visualized. InF. elongatus, of the three pairs of anterior nerves given off from the cerebral ganglia, two are ventral and one is dorsal in disposition. The nerves running posterior from the cerebral ganglia include two pairs of ventral nerves and one of dorsals. Throughout their course the two ventrals of either side are joined to each other by several loop-like connectives. InG. crumenifer, the overall nerve arrangement is somewhat similar to that inF. elongatus; the connectives joining the posterior ventrals of each side are not loop-like. The course of all the nerves and the innervation to the various parts of the body is traced in both the species.