Note 34 — Chapter IX · THE INFLUENCE OF THE CHILD ON LINGUISTIC DEVELOPMENT
Reading edition
In Russian Marfa, Fyodor, etc., we also have f corresponding to original þ, but in this case it is not a transition within one and the same language, but an imperfect imitation on the part of the (adult!) Russians of a sound in a foreign language (Greek th) which was not found in their own language.