Parliament of Australia
From 1901 to 1949, the House consisted of either 74 or 75 members (the Senate had 36). Between 1949 and 1984, it had between 121 and 127 members (the Senate had 60 until 1975, when it increased to 64). In 1977, the High Court ordered that the size of the House be reduced from 127 to 124 members to comply with the nexus provision. In 1984, both the Senate and the House were enlarged; since then the House has had between 148 and 150 members (the Senate has 76).
Father of the Australian Senate
The first Senate was elected on 29 and 30 March 1901. Despite the different election dates, all the members elected to that first Parliament were considered to have had equal seniority. It follows that there could not be a "longest-serving Senator" until only one Senator from the first Parliament was still serving. That occurred on 14 September 1923 with the death of Hon Edward Millen, leaving Sir George Pearce as the sole longest-serving Senator, and thus the first sole Father of the Senate.