A.T. Robertson Commentary Romans 12:5

"so we, who are many, are one body in Christ, and severally members one of another." — Romans 12:5 (ASV)

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 Corinthians 11:23). So εις καθ' εις and in Modern Greek καθεις as a distributive pronoun. But we have καθ' ενα in 1 Corinthians 14:31. The use of the neuter article here το with καθ' εις is probably the accusative of general reference, "as to each one."