''Memoirs of Montparnasse'' is a delicious book about being young, restless, reckless, and without cares. It is also the best and liveliest of the many chronicles of 1920s Paris and the exploits of the lost generation. In 1928, nineteen-year-old John Glassco escaped Montreal and his overbearing father for the wilder shores of Montparnasse. He remained there until his money ran out and his health collapsed, and he enjoyed every minute of his stay. Remarkable for their candor and humor, Glassco's memoirs have the daft logic of a wild but utterly absorbing adventure, a tale of desire set free that is only faintly shadowed by sadness at the inevitable passage of time.