The nervous system of young and adult Amphilina foliacea was studied with immunocytochemical, electron microscopical
and spectrofluorometrical methods. The general neuroanatomy is described in detail. New data on the structure and
development of the brain were obtained. The 5-HT and GYIRFamide-immunoreactivities occur in separate sets of
neurones. The innervation of the reproductive organs is described. The fine structure of 2 types of neurones in the CNS,
a sensory neurone, a ‘glial’ cell type, the neuropile and the synapses are described. The level of 5-HT varies between 0·074
and 0·461 μg/g wet weight. This is the first detailed study of the nervous system of A. foliacea. Earlier data on the structure
of the nervous system in A. foliacea published in Russian are introduced into the discussion. The study provides data that
can be used when considering the phylogenetic position of Amphilinidea.
