Ultrastructure study of the excretory system and the genital primordium of the infective stage of Onchocerca volvulus (Nematoda:Filarioidea).

The electron microscopic investigation of the anterior part of the infective third-stage juvenile of Onchocerca volvulus provides first insights into the structure of the excretory system of this developmental stage of the parasite. The most anterior part of this system consists of a cell process of the syncytial excretory cells. At this height the excretory cells enclose the cuticle-lined excretory channel. The channel is in the process of elongation in the anterior-posterior direction, indicated by cell division in this region. More posteriad an ampulla-like structure is forming in the cytoplasm of the excretory cells. The inner surface of this ampulla is lined with a small number of single microvilli. In this part of the system the cytoplasm of the excretory cells is rich in Golgi bodies and endocytic vesicles. The ampulla has direct access to the exterior by the excretory duct. The excretory duct is a cuticle-lined structure surrounded by supporting fibres of an additional cell. This duct cell connects the excretory duct to the body-wall cuticle at the excretory pore. Adjacent to the region of the excretory system a cell is found that resembles a gland cell. This cell is in close contact to the ventral nerve cord. The genital primordia of the third-stage juvenile consist of several dividing cells. The female genital primordium is seen at the junction of the muscular with the glandular oesophagus and the male primordium can be found at the junction of the glandular oesophagus with the gut.