This chytridiomycete is an endoparasite of nematodes living in the soil. It attacks its victims by means of zoospores; they move chemotactically to the body orifices of nematodes while they appear to reach nematode eggs by chance. Once a spore has penetrated the egg shell, further infective spores are lured chemotactically to the penetration site. The cytology of the spores and the process of encystment has been filmed in the light microscope. Details are shown by means of scanning electronmicrographs. Time-lapse sequences show the entire infection process, the differentiation of sporangia and the release of zoospores.