At the time of its formation no metropolitan municipal corporation shall include only a part of any city, and every city shall be either wholly included or wholly excluded from the boundaries of such corporation. If subsequent to the formation of a metropolitan municipal corporation a part only of any city shall be included within the boundaries of a metropolitan municipal corporation such part shall be deemed to be "unincorporated" for the purpose of selecting a member of the metropolitan council pursuant to *RCW
35.58.120(3) and such city shall neither select nor participate in the selection of a member on the metropolitan council pursuant to RCW
35.58.120.
Any metropolitan municipal corporation now existing within a county with a population of one million or more shall, upon May 21, 1971, have the same boundaries as those of the respective central county of such metropolitan corporation. The boundaries of such metropolitan corporation may not be enlarged or diminished after such date by annexation as provided in chapter
35.58 RCW and any purported annexation of territory shall be deemed void. Any contiguous metropolitan municipal corporations may be consolidated into a single metropolitan municipal corporation upon such terms, for the purpose of performing such metropolitan function or functions, and to be effective at such time as may be approved by resolutions of the respective metropolitan councils. In the event of such consolidation the component city with the largest population shall be the central city of such consolidated metropolitan municipal corporation and the component county with the largest population shall be the central county of such consolidated metropolitan municipal corporation.