6.—A Re-examination of the Central Nervous System of Alderia modesta (Lovén).

Synopsis Alderia modesta (class Gastropoda, order Sacoglossa) has a central nervous system of a type common in the Stiligeridae and Limapontiidae. The visceral loop is short and bears two ganglia, the abdominal and supra-intestinal. Medio-dorsal bodies, probably neurosecretory in function, are present on the cerebral ganglia. They were also found in eight other species of Sacoglossa and latero-dorsal bodies were noted in Oxynoe viridis (Pease) and Lobiger viridis (Pease). Dissections of sixteen species of Sacoglossa showed that the order may be arranged on the length of the visceral loop and the number of ganglia on it. The evolution of medio-dorsal bodies is discussed.