The fine structure of the retrocerebral organ of (Chaetognatha)

A peculiar apparatus consisting of large cells with microvilli, recently described in the cerebral ganglion of the freshwater crustacean Leptodora , has also been found in the cerebral ganglion of Sagitta , a representative of the Chaetognatha. The occurence of cells with microvillous borders in the central nervous system of representatives of two different phyla suggests a role related to functional requirements that the two types of animals have in common.