Abstract

The visceral ganglion and the right parietal ganglion of the African giant snail, Achatina fulica, consists of two hemispheres, each in left and right side, respectively, like a butterfly. The surface of cortex and medulla in the two ganglions are crowded with nerve cells, but nerve fibers form a network at the middle portion. The nerve cells in the cortex and medulla of the visceral ganglion and the right parietal ganglion are classified into the following four classes according to their sizes: giant (above 200 <TEX>${\mu}{\textrm}{m}$</TEX>, in diameter), large (60-70 <TEX>${\mu}{\textrm}{m}$</TEX>, in diameter), middle (30-40 <TEX>${\mu}{\textrm}{m}$</TEX>, in diameter) and small (10-15 <TEX>${\mu}{\textrm}{m}$</TEX>, in diameter) nerve cells, respectively. The giant and large nerve cells are rarely found(20-22 eas. in total) while the middle and small nerve cells are found in large quantities (middle: 400-500 eas., small: 700-800 eas.). In the AB/AY double staining, the giant nerve cell is identified as light yellow cells (LYC), while large and middle none cells as dark green cells (DGC) or yellow green cells (YGC), and small nerve cells as yellow cells (YC) or blue cells (BC), The DGC, which reacts positively to somatostatin immunostain reaction, inhibits the secretion of the growth control hormone. The giant and large nerve cells are identified to do the functions of phagocytosis as well as neurosecretion.