Brugia malayi: ultrastructural morphology of the cuticular surface membranes of adult parasites.

We have obtained and examined several fracture planes close to the surface of the cuticle of adult Brugia malayi by freeze-fracture electron microscopy. We observed three exocytoplasmic and two protoplasmic fracture faces exhibiting the periodic annulations characteristic of the outer layers of the cuticle. The outermost exocytoplasmic fracture face we observed contained small randomly distributed particles and appears to originate from within the epicuticle. The second exocytoplasmic face appeared as a featureless surface representing a nonmembranous proteinaceous structural arrangement adjacent to the epicuticle. The innermost fracture plane was represented by an exocytoplasmic face with a morphology dominated by large particles regularly appearing as organised linear arrays. This fracture plane seems to originate from a membrane-like organisation directly below the annulated proteinaceous layer. The two annulated protoplasmic faces were exposed by two discrete planes of fracture and were complementary to the exocytoplasmic planes. The above observations are considered in terms of the overall structural organisation of the cuticle of adult B. malayi.