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The specimens used in the following investigation were collected in Calcutta in 1891.

Anatomy of the Cervix.—A valve-like structure is formed in the canal of the cervix by means of three strong folds, one of these folds fits into a recess formed by the two other folds, and forms a valve which persists throughout life. It is unlike any other structure of the cervix with which I am acquainted.

Breeding.—A definite breeding season for Macacus rhesus seems to be proved, but it is equally certain that in different parts of the Continent of India the breeding season occurs at different times of the year.

Menstruation.—A congestion of the skin of the abdomen, legs, and tail, a swelling and congestion of the nipples and vulva, and flushing of the face, are all prominent external signs of menstruation. A regular menstrual flow occurs consisting of a viscid, stringy, opaque white fluid filled with granules, and containing also red blood corpuscles, pieces of uterine tissue, both stroma and epithelium, and also leucocytes.

The following classification of the various stages passed through is adopted :—

A. Period of rest. Stage I. The resting stage. B. Period of growth. Stage II. The growth of stroma. Stage III. The growth of vessels. C. Period of degeneration. Stage IV. The breaking down of vessels. Stage V. The formation of lacunas. Stage VI. The rupture of lacunae. Stage VII. The formation of the menstrual clot. D. Period of recuperation. Stage VIII. The recuperation stage.

The surface of the uterine mucosa, which is smooth and semitransparent during Stage I, becomes swollen and opaque during Stage II, and flushed during Stage I I I ; it then becomes highly congested, Stage IV, and dark red spots, due to the formation of lacunae, appear on the surface in Stage V ; when Stage VI is reached, free