Electron microscope study on the developmental stages of Wuchereria bancrofti in the intermediate host: structure of the digestive tract.

The digestive tract and its development from undifferentiated primordia of first, second and third stage larvae of Wuchereria bancrofti are described at the ultrastructural level. In the young first stage larva the future oesophageal cells form a long column surrounding the cuticularized pharyngeal thread. In the midbody region, a small number of cells associated with the inner body represent the intestinal precursor. The large R-cells around the anal vesicle are fully differentiated.--The late first stage larva shows numerous, small oesophageal cells aligned around the pharyngeal thread. The few intestinal cells have greatly enlarged and start to form small lumina between their central membranes. The anal vesicle has increased and is divided in an inner and an outer portion.--In the second stage larva the oesephageal cells gradually differentiate into an inner muscular core around the triradiate cuticularized lumen, and an outer glandular sleeve. The intestinal cells start to form small microvilli at their luminal sides. Large amounts of particulate matter fill the lumina of oesophagus and intestine at this larval stage. The R-cells are still located between the posterior end of the intestine and the inner portion of the anal vesicle. Small, undifferentiated cells around the outer portion of the anal vesicle start to form the rectal tube.--The third stage larva has a fully differentiated digestive tract. The glandular portion of the oesophagus contains an abundance of secretory granules and vacuoles, the intestinal cells show lipid inclusions and long, tightly packed microvilli. The narrow rectal tube opens to the exterior.