these:  The Old English plural of this was thās or thōs. This evolved into those, which came to be used as the plural of that, and it was replaced as the plural of this by thise, formed from this with the plural ending -e, which in due course turned into these. => this
Old English þæs, variant of þas (which became those and took the role of plural of that), nominative and accusative plural of þes, þeos, þis "this" (see this). Differentiation of these and those is from late 13c. OED begins its long entry with the warning, "This word has a complicated history."