Homologous neurosecretory cell groups in the land snail Achatina fulica and the sea slug Aplysia californica.

The right parietal ganglion of the African snail Achatina fulica contains an identifiable cluster of 20-40 white cells with somatic diameters of 80-110 mu. Cobalt chloride injection into these cells revealed an axon projection in the right parietal nerve as well as apparent terminations in the capsule. The cells contain an abundance of electron dense granules 1000-2000 A in diameter which are formed in the Golgi apparatus. The granules stain with Gomori's chrome hematoxylin and paraldehyde fuchsin methods. While most cluster cells showed no "spontaneous" electrical activity, there was a correlation for the active cells between rate of activity and intensity of cell whiteness. These and other data suggest that the cluster cells are neurosecretory. A claim of homology with the "rostral white cells", R3-R13, in the parieto-visceral ganglion of Aplysia is based on a similarity of morphological and electrophysiological features, together with analogous locations in the respective ganglia. It is concluded that the right parietal ganglion of Achatina is homologous with the right half of the parieto-visceral ganglion of Aplysia.