_Salivary Cysts_ are most frequent in connection with the sublingual gland, constituting the so-called ranula. The contents of these cysts are thick and ropy, like the white of egg, and consist essentially of saliva, mixed with mucus and epithelial matter. _Milk Cysts_ are liable to be formed in the mammary gland during lactation. Their size varies. Their contents may be pure milk and perfectly liquid, or mixed with caseous and epithelial substances. _Oil Cysts_ are of rare occurrence, and usually of quite small size. They occur most frequently in the skin or in some glandular organ, especially the breast. Their contents are generally fatty matter, with epithelial and other substances. _Seminal Cysts_ are never of independent growth. They contain a fluid, mostly serum, with the characteristic spermatozoa held in suspension, and only to be detected by the microscope. The only true tumors of this kind are hydroceles of the spermatic cord. _Dermoid Cysts_ are usually congenital, and, in the majority of cases, contain the debris of a blighted ovum, such as hairs, teeth and bone. Sebaceous tumors are a variety of dermoid cysts, and contain sebaceous matter, combined with epithelium and even hair, oil or fat. =B.= _Compound or Proliferous Cysts_ are “characterized by the existence of subordinate cysts, occupied by different organized substances, and giving rise to that peculiar arrangement known as multilocular or polycystic, generally so conspicuous in this class of tumors.” When a number of cysts are crowded together, their walls are frequently absorbed, and irregular cavities, varying in size and shape, are thus formed. Their contents are of the most diversified character. The cyst wall is thin at first, but becomes thicker and firmer in a later stage. Proliferous cysts sometimes take on a malignant character, of the encephaloid or epithelial type, years after their origin. They occur most frequently in the ovary, the mammæ, and the thyroid gland. In the first situation, they not unfrequently attain an enormous size. 2. =Hydatid Tumors.= These tumors occur most frequently in the liver, ovary and uterus. They consist of a distinct sac, enclosing an entozoon, parasite or vesicular worm, “varying in volume between a mustard-seed and a small orange. The entozoon is of a globular figure, of a whitish, semi-opaque appearance, and composed of a vesicle or bladder, filled with serous fluid, and surrounded by a cellulo-fibrous capsule.” Generally a number of them are found in a common cyst. “The contents of the animal are of a clear, limpid character, remarkably saline to the taste, but destitute of odor and coagulability. Between the cyst and the parasite there is commonly a soft, pulpy, dirty-looking substance, the precise nature of which is undetermined. Large hydatids sometimes contain several smaller ones, one within the other.”