A central Problem of Bactrian Phonology, to which Georg Morgenstierne devoted the greater part of one of his last articles, is the origin of Postvocalic t, which is found in a small number of words of disputed etymology. Since OIr. postvocalic t generally gives Bactrian d, as in G[raeeo-Bactrian] οδο, M[anichean Bactrian] 'wd, 'wṭ[ud] ‘and’ <*uta or G κiρδo, M qyrd ‘made’ <*kṛta-,it seems that some oter orgin must be sought for Bactrian t—unless, indeed, G δ and τ may be regarded merely as alternative notations of [d], as has been Proposed. Such a Possibility was first suggested by G oτo ‘and’, which accoriding to W. B. Henning is ‘not differne from οδο ’, and which I. Gershevitch has explained either as a historical spelling or as a generalized sandhivariant of οδο. However, a crucial objection to the identifieation of οδο and οτο lies in the fact, the implications of which have not yet been fully appreciated, that they differ not only in form but also in function.