ULTRASTRUCTURAL OBSERVATIONS ON THE NERVOUS-SYSTEM AND THE SENSORY ORGANS OF THE INFECTIVE STAGE (L3) OF ONCHOCERCA-VOLVULUS (NEMATODA, FILARIOIDEA)

A detailed morphological investigation of the sensory organs and the n ervous system of the third juvenile stage of Onchocerca volvulus was p erformed at the ultrastructural level. A complex system of different r eceptor cells is found at the anterior and posterior end of this devel opmental stage. The eight papillae are arranged in two concentric circ les consisting of two types of morphologically different receptors. Ac cessory nerve processes end free in the tip of the head. The paired am phids contain nine dendritic processes and accessory axons are seen in the surrounding cells. The basic structure of the amphids and of the circumoesophageal nerve ring is similar to that of other filarial nema todes. Two presumably neurosecretory cells are associated with the ner ve ring. The reticular cytoplasm of these cells merges with the rough- surfaced endoplasmic reticulum of the lateral hypodermal chord. The pa ired phasmids at the posterior end of the developmental stages consist of single modified cilia that are embedded in an electron-dense mass. The receptor cell has access to the outside by a channel ending with a cuticular pore.