THE ULTRASTRUCTURE OF THE ANTERIOR END OF MALE ONCHOCERCA-VOLVULUS - PAPILLAE, AMPHIDS, NERVE RING AND FIRST INDICATION OF AN EXCRETORY SYSTEM IN THE ADULT FILARIAL WORM

A detailed morphological investigation of the anterior sensory organs, the nerve ring and a glomerulus-like structure in male Onchocerca vol vulus was performed by means of electron microscopy. The 8 head papill ae are arranged in the common 4 + 4 pattern of most filarial worms in circles around the mouth opening. The amphidial openings are found bet ween the circles of inner and outer papillae on both sides of the mout h. Inside, several additional nerve axons are seen in the tissue of th e anterior tip not related to one of the identified papillar structure s. The inner and outer papillae exhibit a remarkably different fine st ructure, and are part of a complex system of at least 2 different rece ptor cell types at the anterior tip of the worm. The amphidial channel contains 8 modified cilia; accessory axons are associated with the cy toplasm of the sheath cell. The anterior nerve ring of male worms is l ocated about 150 mu m posterior from the outermost tip of the head reg ion. It consists of several fibres coiled around the oesophagus. The c omparison of the fine structure of the central nervous system did not show the expected morphological differences associated with the hetero geneous age distribution in the natural worm population. This was in c ontrast to previous findings with respect to tissues in different part s of the worm. The study also provides the first evidence that suggest s the existence of an excretory organ in a filarial worm in the region of the anterior nerve ring. Paired glomerulus-like structures in the lateral chords and a canal formed by a projection of the basal zone of the cuticle were identified.