The life cycle of a Haplosporidium found in the aquatic snails of the Douglas Lake region of Michigan has been studied. It represents the first report of Haplosporidium in fresh water snails and is the first record of this parasite from North America. Morphologically indistinguishable spores have been recovered from unrelated snail hosts indicating that the sporozoan is not host-specific. The protozoan is found in a number of species of fresh water snails as cytozoic and histozoic parasites limited to the digestive glands. ...The present paper is a description of a species found in fresh water snails, with a discussion of some stages in the life cycle that have been confusing to the previous workers. The fact that the development stages are limited to the digestive gland of the snail makes it possible to interpret the relationships of some stages in the life cycle more clearly than in the similiar stages that were found as coelozoic infections.