Where, by or under this Act, any act, other than the making of an affidavit, is required to be done before the Registrar by any person, the act may, subject to the rules made in this behalf, be done instead of by that person himself, by a person duly authorised in the prescribed manner, who is—

(a) a legal practitioner, or

(b) a person registered in the prescribed manner as a trade marks agent, or

(c) a person in the sole and regular employment of the principal.