An enlarged aggregate of apocrine glands on the chest of karyotype I owl monkeys.

A firm circumscribed umbilicated mass in the middle of the chest, overlying the cephalad portion of the sternum, was an incidental finding in the skin of three males and one female from a group of eight (four male and four female) aged karyotype I owl monkeys (Aotus trivirgatus) released to our laboratory from the breeding colony of the Walter Reed Army Institute of Research (WRAIR). Light microscopic examination of each mass revealed an enlarged aggregate of apocrine glands which was interpreted to be the result of hyperplasia. Some degree of enlargement of the aggregate of glands was observed on all adult male karyotype I owl monkeys recently examined at WRAIR.