The ovum is known to pass through the Fallopian tube of the sow in approximately 3 days. The author studied 168 tubes, from 84 sows whose ovaries bore corpora lutea under 7 mm. diameter. In 52 specimens (104 tubes) ova were washed out. The ova pass quickly through the ovarian end of the tube, spend about 2 1/2 days in the ampulla, and then progress fairly rapidly to the uterus. The first polar body has been given off before the ovum enters the tube. Fertilization occurs in the ovarian end, and nearly all the ova found in the uterine half of the tube are in stages from 2 pronuclei to 2-8 blastomeres. The segmenting ovum enters the uterus in a stage ranging from 4 blastomeres to a many-celled morula, never as a blastula. Transport through the tube is believed to be dependent wholly on tubal muscle and cilia. The time required for the passage seems unrelated to length of tube or relative size of ovum and tube, in various species, but is quite constant for all the species of a given order. The author gives a full review of the literature.