It has been rather generally accepted that colloid cysts of the third ventricle are derived from persisting remnants of the paraphysis2' 5 as first suggested by Sj6vall6 in 1909. The paraphysis is a variety of extraventricular choroid plexus found best developed in adult forms of the ganoid fishes and certain amphibia, but is present in the embryos of all vertebrates, including man. This struct...
