1. =Cystic Tumors.= These are of very frequent occurrence, and may acquire an extraordinary size. Their structure may be simple or very complex, and we may accordingly divide them into simple or barren, and compound or proliferous cysts. They may be new formations or, as in most cases, merely hypertrophies. They occur in nearly every organ and tissue of the body, but are most frequently met with in the skin and mucous membranes, the glandular organs, and in the subcutaneous cellular tissue. =A.= _Simple Cysts_ generally consist of a thin sac or cyst filled with contents, varying according to the structure and function of the affected part. The cyst itself may be solitary or multiple, generally composed of a single layer, its external surface being rough and adherent to the surrounding tissues, while the internal surface is shining or glossy, and in immediate but loose contact with the contents of the tumor. According to the nature of their contents, we may find the following varieties of simple cysts: _Serous Cysts._ Their contents are generally of a thin, watery character, slightly saline in taste, and consisting largely of albuminous material. The walls are thin, and at first translucent; as they grow older they become thicker and denser. _Mucous Cysts_ generally contain a thick, ropy, glutinous material, intermixed with epithelial matter. Sometimes the contents are thin and clear; occasionally they resemble the fluid contained in a synovial bursa. Such tumors occur chiefly in connection with the mucous membranes, are generally spherical or pyriform in shape, and may attain the size of a fœtal head. _Synovial Cysts_ are generally small in size, rounded, globular, or hemi-spherical in shape, with contents of a serous, mucus, glutinous, colloid, or of a jelly-like consistence, and of a whitish, opaque appearance. They occur generally in the synovial sheaths of the tendons of the wrist, and on the front of the patella. The most characteristic types of synovial cysts are those known as ganglions and bursæ. _Colloid Cysts_ are rarely met with as independent structures; they usually occur as accidental constituents of various kinds of morbid growths. Their contents vary in consistence between mucus and the thickest jelly, “their color being generally whitish or pearl-like, not unfrequently blended with shades of pink, yellowish-brown, or olive-green.” _Sanguineous Cysts_, or hæmatomata, may be entirely new formations, or may occur in a normal cavity. Their contents may consist either of pure blood or of blood mingled with serum and other substances. “The cyst wall is usually very thin and smooth; but in some cases the inner surface has a peculiar fasciculated appearance, not unlike that of the right auricle of the heart.” The cyst is commonly small, and of a rounded or hemi-spherical shape.