Casual vacancies.- All casual vacancies among the members

(other than ex-officio members) of the Board or any Committee constituted under this Act shall be filled up, as soon as may be, by election, nomination or appointment, as the case may be, and the person elected, nominated or appointed to a casual vacancy shall hold office so long only as the member in whose place he is elected, nominated or appointed would have held it, if the vacancy had not occurred.