This theory proposes that schizophrenic symptoms are due to the presence of myelinated interhemispheric nerve fibres which link functional areas in the brains of schizophrenics which are not connected in normal subjects. The role these fibres would have in the production of schizophrenic symptoms is examined in the context of recent neuroanatomical and neurophysiological findings in schizophrenics. The functional emergence of these fibres is examined phylogenetically in conjunction with central nervous system myelination. Genetic biochemical and therapeutic implications are considered.