λέγοντος τοῦ Πιττακοῦ κτἑ.: epexegetical of πρὸς τὸ τοῦ Πιττακοῦ κτἑ.; hence the asyndeton. See on 340 e.
γενέσθαι μέν: should strictly have been followed by εἶναι δέ or διαμένειν δέ (cf. 344 b, 345 c), but it is followed in 344 a only by οὐ γὰρ εἶναι κτἑ. with anacoluthon.