Answer:
Before the 1870s there were provincial Governments, and then a national government was formed.
Many changes have been made - universal suffrage, the abolition of votes only for landholders, the institution of 1 man 1 vote system, and in recent decades we moved from the 'first past the post' voling system to a Mixed Member Proportional voting system. (MMP).
This is to be reviewed later this year in conjunction with the general election in November 2011.