The Tutors are immediately responsible for the general supervision of the students in the College: the actual teaching is done by Lecturers in the various subjects, who have special apartments, "Lecture Rooms," provided in every College for their purposes. Every student has to attend a certain quota of lectures, but otherwise is very much left to educate himself, his progress being checked by periodical College examinations, in addition to those required by the University to be passed before he can be admitted to a Degree. The lowest Degree is that of B.A. (Bachelor of Arts). Three years after attaining this a man may proceed to become M.A. (Master of Arts), when he ceases to be "in statu pupillari," and is no longer subject to the authority of the Proctors. These officers perambulate the town after dark to punish University wrong-doers, usually by a fine of 6_s._ 8_d._, or some multiple of that sum, the unit being a survival from mediaeval numismatics, as equivalent to half a "Mark." More serious offences are met by "Rustication," for a Term or a year, during which the offender may not show himself in Cambridge, and, in extreme cases, by expulsion from the University altogether. These punishments can also be inflicted by the authorities of each College on the students of that College. But in this domestic forum, for smaller offences the place of fines is taken by "gating" for a certain period, during which the nocturnal enclosure of the culprit begins at some earlier hour than usual. As a regular rule the College gates are shut at ten p.m., after which no outsider (student or visitor) may enter, and no inmate (under the Degree of M.A.) pass out; though to students already out uncensured admission is given until midnight. Once inside the gates the student is under no obligation to keep to his own rooms, but has the run of the College all night. He is bound, however, to spend his nights within the walls, and not even for a single night may he be absent without a duly signed _exeat_ from the College authorities giving him leave. And, as he must be in residence when they require it of him, so is he also forbidden to be in residence at such seasons as they bar; during the greater part of each Vacation, for example, comprising half the year.