examination, shall assign the rank of the applicants, according to the
degree of merit and fitness shown; and he who stands at the head of the
list shall have the choice of vacancies in the particular department
or branch for which he was examined, and so on down the list to the
minimum of merit fixed by the Board, beyond which no certificate shall
be given. The Board may, if they see fit, assign the right of seniority
as a result of the first examination, or may require a further
examination, the result of which shall determine seniority.