Dynamics of the filarial surface.

The surface of the filarial worm consists of an extracellular cuticle which overlies the outer plasma membrane of the hypodermis. The cuticle is permeable to a wide range of molecules of low molecular weight, and L-amino acid and D-glucose uptake occurs transcuticularly by active transport and diffusion in physiologically significant amounts. Transport mechanisms are associated with the plasma membrane of the hypodermis, and the cuticle may be considered an 'unstirred layer' distal to the transport loci. The outermost layer of the cuticle, or epicuticle, consists of a lipid bilayer which differs from a typical plasma membrane. There is no conclusive evidence for turnover of the epicuticular materials between the larval moults and in the adult stage. It is proposed that the filarial surface does not show the dynamic properties associated with the surface membranes of parasitic cestodes and trematodes.