This paper describes the position and time of postnatal closure of a vessel from the pulmonary artery to the aorticopulmonary glomus (carotid body-like) tissue. Nine prenatal and eight postnatal kittens (killed at 12 hours, and 8, 12, 16, 30, 42, 60 and 90 days) and 50 adult cats were examined. The vessel arose from the root of the right pulmonary artery and had ascending and descending branches. The latter supplied the aorticopulmonary glomus tissue and mingled with vessels arising from the root of the coronary arteries — usually the left. In two prenatal cats an actual anastomosis was demonstrated. There was no change in the intramural part of the branch of the pulmonary artery in kittens less than 16 days old. The vessel was partly closed by cellular proliferation by the sixteenth day and was almost certainly occluded by the forty-second day. It was not patent in any animal more than 42 days of age. In the adult cat, the aorticopulmonary glomus tissue was less cellular than in the fetus. It is suggested that the communication between the branch from the right pulmonary artery and the coronary arteries through chemoreceptor tissue may have functional significance.