Mrs. P., aged 20, primipara, Hebrew, with negative previous and family histories, presented herself for examination, when six months pregnant, and the following observations were made: She was a tall, slim woman, fairly well nourished but somewhat anemic. Abdominal and vaginal examination showed a six months' pregnancy. The breasts were large and pendulous, the lower borders reaching almost to the level of the umbilicus. The nipples were well formed. Along the outer borders of both breasts, but especially the left, definite, separate masses of breast tissue could be outlined, so-called supernumerary breast tissue. In the upper, outer quadrant near the border of the right breast, a rounded, firm, slightly lobulated tumor, the size of a walnut, was seen. This was freely movable under the skin and over the underlying muscle. The patient complained of very little pain, and stated that she noticed the tumor about three weeks previously. About three