GENERAL ANATOMY AND HISTOLOGY OF THE NERVOUS-SYSTEM IN ACHATINA-FULICA

The nervous system of Achatina fulica is composed of 13 ganglia : a pa ir of buccal ganglia, a pair of cerebral ganglia, a pair of pleural ga nglia, a pair of parietal ganglia, a pair of pedal ganglia, a pair of tentacular ganglia and a single visceral ganglion. All ganglia give ri se to many nerve branches which supply the snail body. They are surrou nded by two layers of connective tissues: the thick outer layer and th e thin inner layer connective tissue. Within the ganglia, there are ne rve cells or ganglionic cells of four sizes: (1) the small cells which have the diameter of < 20 microns, (2) the medium-sized cells which h ave the diameter of 20 - 39 microns, (3) the large cells which have th e diameter of 40 - 99 microns, and (4) the giant cells which have the diameter of > 100 microns. In addition, there are masses of very small cells or globuli cells which have the diameter of 5 - 7 microns in th e cerebral ganglia and the tentacular ganglia. Furthermore, in the cer ebral ganglia, there is a group of neurosecretory cells which are char acterized by a round heterochromatic nucleus and 4 large vacuole. Simi larly, neurosecretory cells or collar cells were found around the fing er-like projections of tentacular ganglion. These cells contain small round nuclei and their Cytoplasm is full of granules and droplets.