The migration of Schistosoma mansoni through mouse skin and the morphology of integument and associated structures of the parasites were studied with an electron microscope. The epithelium of the schistosomule was covered by a fine granular envelope, which appeared to be an altered form of the pericercarial envelope of the free-living cercaria. Basal corpuscles with prominent flagella used for locomotion through fluids emanated from the medullary parenchyma at frequent and regular intervals. The flagellum was composed of nine radial plus two central pairs of axial filaments. The basal portion of the integument was highly invaginated. Cytoplasmic extensions were invested with a complex of microtubules that appeared to represent a cytoskeletal system. Assorted inclusions believed to represent secretions were observed in the integument, cytoplasmic extensions, “cavernous cisterns,” and in areas resembling storage sites. The earliest specimens of migrating schistosomules were oblique to the surface of the skin, burrowing between the keratinous and intermediate layers. Fragments of granulated keratin were scattered in the wake of the advancing schistosomule, suggesting passage through this layer accommodated by a chemical lysis, not merely a mechanical phenomenon. Migration through the intermediate and basal layers involved injury to the desmosomes, plasmalemma, and cytoplasmic organelles. The nuclei appeared initially refractory to the effects of the schistosomule and showed degenerative changes only after the cytoplasma was almost completely effaced. After the epithelial cells were eroded, the subjacent basement membrane was exposed. This structure represented a major barrier and temporarily delayed migration of the schistosomules. Within the dermis, however, the characteristic banding pattern of individual collagen fibrils began to fade, and swelling and fragmentation were observed. This suggested specific collagenase activity.
WRAIR Composite Drug Screening Unit, U. S. Army Medical Command, Japan, APO San Francisco, California 96343.