The Directors of the Massachusetts Penitentiary, in their last Report, say, that the erection of an additional building, within the Prison yard, where each convict may be provided with a separate apartment for lodging, has long been a favorite object with the government of this institution. The Commissioners of the Connecticut Legislature, say, that the great and leading objection to Newgate, is the manner in which the prisoners are confined at night--turned in large numbers into their cells, and allowed an intercourse of the most dangerous and debasing character. It is here, that every right principle is eradicated, and every base one instilled. It is a nursery of crime, where the convict is furnished with the expedients and shifts of guilt, and, with his invention sharpened, he is let loose upon society, in a tenfold degree, a more daring, desperate, and effective villain. The superintendent of the New York Penitentiary, ARTHUR BURTIS, Esq. speaking of the crowded state of the night rooms, said, how can you expect reformation, under such circumstances? As well might you kindle a fire, with a spark, on the ocean, in a storm. If a man forms a good resolution, or feels a serious impression, it is immediately driven from him in his night room. The superintendent of the New Jersey Prison, FRANCIS S. LABAW, says, the greatest improvement, that has been made, or can be made, in Prison Discipline, is by solitary confinement. The solitary cells in this Prison, in which one fourth part of the whole number of prisoners are placed under sentence of the Court, have answered all the purposes, which it was ever expected they would, so far as trial of them has been had. No person, who has been once confined in them, has ever returned to the Prison. The Senate of Pennsylvania say, for want of room, the young associate with the old offenders; the petty thief becomes the pupil of the highway robber; the beardless boy listens with delight to the well told tale of daring exploits, and hair breadth escapes of hoary headed villany, and from the experience of age, derives instruction, which fits him to be a terror and a pest to society. Community of design is excited among them, and, instead of reformation, ruin is the general result. The superintendent of the Virginia Penitentiary, SAMUEL O. PARSONS, says, I consider separating convicts at night, of all others, the most important feature in the Penitentiary system of punishment, and one, which should every where claim the first consideration in erecting such institutions. With the opinions thus expressed, of the practical men placed at the head of these institutions, the opinions of the governors of the respective States, of the judges, and legislators, and benevolent men, so far as they have been expressed or known, perfectly coincide. Governor PLUMER, of New Hampshire, says, effectual measures should be adopted to separate, in the Penitentiaries, old offenders from the young and inexperienced.