Into the cloaca, very near the anus, open two glands of fairly large size that Rathke called _musk glands_. These glands lie outside of the pelvis between the side walls of the cloaca and a large muscle that surrounds this part of the body. They have an oval form and open usually from their anterior end, sometimes just caudad to this, by a short, fairly wide, slit-like opening which has an anteroposterior direction. The walls of the glands are made up of three closely associated layers of connective tissue, the inner one being thrown into folds. Since these layers contain no muscle fibers the secretion of the gland is probably squeezed out by contraction of the circular muscles of the cloaca. Usually the cloacal glands are stretched full by a thick, yellowish mass that smells strongly of musk. The part of the cloaca caudad to the pelvic opening has a differently arranged musculature from the more anterior region. It consists of two separate pairs of striped muscles that surround the musk glands on the outer side. The first pair form a fairly broad, moderately thick ring muscle next to the anus that is attached anteriorly to the pubis and posteriorly to the second hæmal process. When these muscles draw together they narrow or completely close the anal slit. The muscles of the other pair are broader but thinner, and extend in a general dorso-ventral direction. Anteriorly, above the cloaca, they are united with each other, but posteriorly they separate and, with the above ring muscle, are inserted on the second hæmal arch. Judging from their attachment they widen the anal opening laterally. THE HISTOLOGY OF THE ENTERON OF THE FLORIDA ALLIGATOR It has long been known that the sea lamprey, _Petromyzon marinus_, during the spawning season, when the body is distended with eggs, takes no food, and that the digestive tract during this period shrivels up until it is reduced to a mere thread. This condition doubtless obtains in other forms as well, though it has not been actually observed by the writer elsewhere. A number of small alligators that were kept alive in the laboratory for a year or more caused the writer to wonder whether any very marked change had taken place in their digestive tracts during the months they took no food. In captivity, especially if the water in their tank be kept cold, alligators may refuse food for five or sixth months. Whether, during the winter months, in their native haunts, they entirely cease feeding, the writer has had no opportunity to observe, though it is popularly reported that such is the case. The first alligator from which tissues were taken was about a year and a half old, and measured eighteen inches in length. It was killed in March after a fast of several months, probably four or five, possibly more, though it was not in the writer’s possession for so long a time. [Illustration: FIG. 35. OUTLINE OF DIGESTIVE TRACT