SUMMARYThe development of spores and eggs of Zonaria farlowii was studied with light and electron microscopy. Oogonia require a lunar month to develop and are produced in periodic crops. The sporangia, on the other hand, are longer in developing and on a particular plant do not become mature all at the same time. Differences in size, content, and products of sporangia and oogonia have been found. One of the quantifiable differences is in the amount of osmiophilic substance, presumably oil, present in the 2 cells. This substance is more abundant in the sporangium, a cell which produces 8 reproductive spores. These differences are particularly interesting since the embryology of sporic and zygotic germlings has been found to be identical, while ontogeny of spores and eggs differs. The findings of this study are discussed in view of possible relationships between microstrtrclitral features of spores and fertilized eggs and their subsequent development.