The Cyst-Wall consists of densely-reticulated areolar tissue, the internal layer constituting an epithelium of cells or nuclei. In large cysts this is, for the most part, absent, and the internal layer generally presents a nucleated, structureless, or striated blastema, at the circumference of which the oval nuclei are in the act of splitting into fibres, in the direction of their long axis. On examining a section of the internal layer of a cyst-wall, from a part furnished with vesicles (secondary cysts), we obtain a view like that presented by the cortical substance of a kidney affected with cyst-formation, to the consideration of which we shall shortly have to recur. The same nidu3 often contains concurrently incrustations, in some instances remarkable for their size and figure. On examination, the excrescence appears as a hollow growth, consisting of a transparent structureless membrane, studded with round or oval nuclei, often striated, especially at the pedicle, and breaking up into delicate fibrils, with numerous spheroid protuberances. These become developed into pouches, mostly bulb-shaped at the extremity, and by throwing out secondary protuberances and pouches, complete the branchlets and twigs of the excrescence. They may be invested with the epithelium of the cyst-wall, or even uninvested. They are furnished with conspicuous bloodvessels, which, running along the protuberances, describe extensive arches and anastomoses, and frequently become the seat of aneurismal dilatations, or the source of hemorrhagic effusion into the cysts. In their interior they contain nuclei in various numbers, and along with these, especially near the blind extremity of the branchlets, growths which turn out to be young cysts.

These young cysts dilate into those spoken of as cognizable with the naked eye.

The minutest excrescences appear as simple, smooth, or tuberous hollow bulbs. The internal layer of a cyst-wall, presenting the reticulated texture described (5), appears, when magnified, in the form of elongated, round, angular, distended meshes, through which the simple, smooth bulbs penetrate as they grow. The cancellated framework, contained within the described vesicles, consists of a hyaline, structureless membrane, studded with nuclei. It has unquestionably arisen out of the fusion of several bulbs.