first class shall become vacant at the expiration of the third year three years, and the places of those of the second class at the expiration of the sixth year six years, from the beginning of their term of service; and afterwards the places of senators shall become vacant at the expiration of six years from the beginning of their term of service. (3.) In the case of each State, where the number of senators to be divided is an even number the number of senators in each of the two classes shall be equal and where the number of senators to be divided is an odd number the number of senators in the first class shall be one more than the number in the second class. (4.) Sub-section (1.) of this section applies to senators included in the first class, but the term of service of senators included in the second class expires upon the expiry or dissolution of the first House of Representatives to expire or be dissolved after they were chosen. (5.) Where, since the election of senators for a State following a dissolution of the Senate but before the division of the senators for that State into classes in pursuance of this section, the place of a senator chosen at that election has become vacant, the division of senators shall be made as if the place of that senator had not so become vacant and, for the purposes of section fifteen of this Constitution, the term of service of that senator shall be deemed to be, and to have been, the period for which he would have held his place, in accordance with this section, if his place had not become vacant. (6.) Subject to sub-section (7.) of this section, in the case of a senator holding office at the commencement of this section— (a) if his term of service would, under the provisions in force before that commencement, have expired on the thirtieth day of June, One thousand nine hundred and seventy-seven, his term of service shall expire upon the expiry or dissolution of the second House of Representatives to expire or be dissolved after that commencement or, if there is an earlier dissolution of the Senate, upon that dissolution; or (b) if his term of service would, under the provisions in force before that commencement, have expired on the thirtieth day of June, one