c 



D 



Fig. 19.16. Photomicrographs of living embryos of monkeys showing early stages 

 of division. The fertilized ovum was washed out of the tube, cultivated in plasma 

 and its growth recorded in micro-moving pictures. 



The numbers of hours include the time between ovulation and fertilization, and 

 the period of cell division which follows. 



A, two-cell stage, about 29 hours after ovulation, the actual escape of the egg 

 from the ovary. B, three-cell stage, about 36!/2 hours. C, four-cell stage, about 

 31 V2 hours. D, five-cell stage, about 48 '/i hours. E, six-cell stage, about 49 hours. 

 F, eight-cell stage, about 50 hours. (After Lewis and Hartman. Courtesy, Patten: 

 Human Embryology, ed. 2. New York, The Blakiston Co., 1953.) 



381 



