INTRODUCTION. ix Old Syriac nor with the Peshitta. The most probable explanation is the conjecture of Lagarde with regard to the Apostolic Constitutions1, which are an amplification of the Didascalia, viz. that the immediate source from which the author drew was a Gospel Harmony. Professor Nau says of the Didascalia "elle parait ignorer 1'Evangile de S. Jean" (La Didascalie, footnote, p. 119). Nevertheless it will be seen from our list of quotations that there are several which can only be taken from the Fourth Gospel. I have endeavoured to classify all the quotations according to the best of my judgment as follows, on p. xiii. 1 See Lagarde, Const. Apost. p. vii (London, 1862).