Romanos 12:5

And severally

(το δε καθ' εις). A difficult late idiom where the preposition καθ' (κατα) is treated adverbially with no effect on the nominative case εις like υπερ εγω (2 Corintios 11:23). So εις καθ' εις (Marco 14:19) and in Modern Greek καθεις as a distributive pronoun.

But we have καθ' ενα in 1 Corintios 14:31. The use of the neuter article here το with καθ' εις is probably the accusative of general reference, "as to each one."