Unilocular cysts occasionally attain an immense size at the same time that their walls remain thin and supple. In some of these instances, the fluid continues to the last, of a truly serous character; while in others, it becomes more or less glairy or mucilaginous. Sometimes the walls of the cysts have been found to have undergone calcareous degeneration. _The cysto-sarcoma_, occurs as an isolated, globular or oval, and more or less movable cyst; or there are numerous growths of this kind, varying in size from a pin’s head to a hen’s egg. The inner surface is smooth, or it presents a broad-based, lobulated, cauliflower growth or warty excrescences, and the substance of the surrounding gland is indurated and atrophied. A retraction of the nipple may also be observed. A transverse section shows a double sheath: one proper to the cyst, and the other the result of condensation of the adjoining textures. The contents are either fluid, of a limpid, opalescent, non-albuminous, or a grumous, brownish, highly albuminous character; or solid, approaching the character of a fibroid deposit, composed of a pale, compact substance, traversed by undulating fibrous lines, which imperfectly divide it into lobes of various sizes and shapes. _Hydatid cysts_, containing the echinococus, occur in the female breast. The tumor is firm to the touch, and contains a clear fluid, in which the microscope detects the tenacula of the echinococus, the animalculum itself being attached to the internal wall of the cavity. _Fibrous_, _cartilaginous_ and _osseous tumors_, are of doubtful or very rare occurrence. =Carcinoma.= Cancer affects the mammæ more frequently than any other organ of the body. The age from forty to fifty years seems most liable to its occurrence. According to Dr. Walshe, the left side is more frequently affected than the right, and both are but rarely involved. All varieties of carcinoma have been met with in the breast; but scirrhus is by far the most frequent form in which it occurs primarily. The encephaloid variety is generally engrafted upon the scirrhus, although it may also be primary. The colloid form is the most rare. _Scirrhus_ appears as a hard, lobulated tumor, imbedded in the adipose tissue of the gland, causing adhesion to the skin and retraction of the nipple. Although at first movable, it soon becomes firmly adherent to the subadjacent parts, and involves more or less the gland tissue, the muscles of the thorax, and the adjoining glands. Instead of an isolated tumor, there may be an infiltration of the various structures of the part from the commencement. It will then have an ill-defined outline, sending out branches into the adjacent tissues, and involving in its mass the lacteal tubes and lymphatics. These become contracted and flattened into many bands, giving a peculiar appearance to this form of mammary cancer not observed in any other.