"Certificate" means a certificate of exemption from military service under this Act; "The Militia Act" means the Militia Act and all regulations and orders made under the authority thereof; "The Army Act" means the Army Act for the time being in force in the United Kingdom and all regulations and orders made under the authority thereof; "Regulations" means regulations made by the Governor in Council under the authority of this Act and directions made under such regulations; "Minister" means the Minister of Justice; "Tribunal" means a tribunal constituted under this Act. 2. (1) Every male British subject who comes within one of the classes described in section three of this Act, and who,- (a) is ordinarily resident in Canada; or, (b) has been at any time since the fourth day of August, 1914, resident in Canada, shall be liable to be called out as hereinafter provided on active service in the Canadian Expeditionary Force for the defence of Canada, either in or beyond Canada, unless he (a) comes within the exceptions set out in the Schedule; or, (b) reaches the age of forty-five before the class or subclass to which he belongs, as described in section three, is called out. Such service shall be for the duration of the present war and of demobilization after the conclusion of the war. (2) Nothing in this Act shall prevent any man from voluntarily enlisting in the Canadian Expeditionary Force, so long as voluntary enlistment in such Force is authorized. 3. (1) The men who are liable to be called out shall consist of sic classes described as follows:- Class 1-Those who have attained the age of twenty years and were born not earlier than the year 1883 and are unmarried, or are widowers but have no child. Class 2.-Those who have attained the age of twenty years and were born not earlier than the year 1883 and are married, or are widowers who have a child or children. Class 3.-Those who were born in the years 1876 to 1882, both inclusive, and are unmarried, or are widowers who have no child.