Light and electron microscopic investigation of the sensory cell bodies in the epidermis of the foot of the snail Helix pomatia L.

Abstract

Light and electron microscopic studies were made on the receptor cells in the sole of the snail Helix pomatia. The cell bodies of the primary receptor cells, which can frequently be found in columnar or ganglion-like groups are situated at different depths below the basal lamina. The perikarya of the sensory cells usually measure 12 micrometers by 8 micrometers. Their nuclei are usually invaginated and contain large amounts of marginal heterochromatic substance. The nucleus usually measures 8 micrometers by 6 micrometers. The cytoplasm contains a well-developed Golgi apparatus consisting of several stacked lamellae surrounded by clear and dense-core vesicle. There are differences between cells in the amount of smooth and rough endoplasmic reticulum, in the free ribosomes and in other cytoplasmic elements. The axonal processes of the sensory cells are generally thin and connected to the subepithelial plexus. There are axonic swellings containing a mixed vesicle population, some of them near the muscle cell processes. We failed to find typical axo-axonic synaptic connections in the subepithelial nerve plexus as well as in motor connections within the muscle cell processes. On the basis of the ultrastructural features of the vesicles and other organelles we failed to classify different types of sensory cells. The ultrastructural difference between sensory cell bodies may be explained with a presumptive differentiation process.