The Cell Theory is criticised and an alternative version proposed. It is suggested that the notion of a sponge-like, spongioform, cell (7) might be preferable to the classical notion of a membrane-bound cell. This would allow consideration of the probability that cells behave like sponges and procure their material and metabolite requirements entrained in a convected flow of water past their internal membrane systems. I shall consider some deductive consequences of this alternative in a companion article (1). The Cell Theory, however, formulated on the basis of a membrane-bound cell, specifically excludes the possibility of convective flow in and out of cells. For that reason, the metaphysical and historical foundations of Cell Theory are re-examined, the cases for the physicochemical viewpoint as against the teleological viewpoint further discussed, and the relationship of them to the notions of 'cell', 'membrane', and 'diffusion' looked into all over again. It is concluded that there is more evidence, from light and electron microscopy, for a spongioform cell than for a balloon cell.