Two relative (or conditional) clauses each with μέν may be followed
by two demonstrative clauses each with δέ; but the second δέ is usually omitted, and there are other variations. Thus, ὁπόσοι μὲν . . . οὗτοι μὲν . . . ὁπόσοι δὲ . . . τούτους ὁρῶ
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].