The glandular cysts probably originate from the tubes of Pflüger. It will be remembered that in the embryo the ovary contains many epithelial tubules derived from the germinal epithelium that covers the surface of the ovary. These are the tubes of Pflüger. In the process of development they become converted into Graafian follicles. Abnormally they persist, and have been found in the ovary at an advanced age, as late as the seventy-fifth year. In the newborn infant these tubes have been found cystic--the size of a pea. Such cystic degeneration of persistent tubes of Pflüger is the probable origin of glandular cysts of the ovary. According to this view, all such cysts are due to a congenital defect. Some are perhaps formed congenitally, and remain stationary or develop in later life. The central cells of the tubes of Pflüger soften and become liquefied, and the tube becomes distended into a small pouch lined with primitive glandular epithelium. The outer surface of a typical glandular cyst of the ovary presents a smooth, glistening, silvery appearance. This appearance is subject to considerable variation according to the character of the cyst-contents, the thickness of the wall, and the inflammatory and necrotic changes that have taken place. Sometimes there are ocher-colored or brownish spots upon the surface. The surface of the cyst is often lobulated, from the presence of smaller cysts or a collection of secondary cysts in the wall. The _wall_ of the cyst is composed of fibrous tissue containing elastic and unstriped muscular fibers. Traces of normal ovarian tissue may be discovered in the cyst-wall. Sometimes a corpus luteum is found in the wall of a cyst of large size, showing that ovarian follicles may ripen and rupture, and that conception may take place even though the ovary is grossly diseased. The thickest portion of the cyst-wall is that in the region of the pedicle. The thinnest portion is usually opposite the peduncular attachment. By careful dissection the wall may generally be divided into three layers--an external and an internal layer of fibrous structure, and a middle layer of loose connective tissue. This differentiation is best marked in the region of the pedicle. In the thinnest part of the cyst the coats become blended into a thin, homogeneous, fibrous structure. The outer surface of the cyst is covered with a layer of endothelial cells. This is not a peritoneal investment. It is intimately connected with the outer fibrous coat of the cyst, and cannot be stripped off. In this respect these cysts differ from some hereafter to be described, in which there is a distinct detachable peritoneal covering. The blood-vessels of the tumor are distinguished throughout the fibrous wall. When three lamellæ are present, the large arteries are found in the middle layer. Lymphatics, often of large size, are also found in the cyst-wall.