John Spangler Nicholas, an American biologist, was born on 10 March 1895 in Allegheny, Pennsylvania. He was the only child of Elizabeth Ellen Spangler, a teacher, and

Physician and pathologist Elizabeth Maplesden Ramsey was a member of the Carnegie Institution of Washington (CIW) for thirty-nine years. The affiliation began in 1934, when Ramsey discovered what was assumed to be the youngest-known embryo at the time, and donated it to CIW’s massive embryo collection. After studying embryos, Ramsey focused her research on placental circulation in primates.

Otto Mangold was an early-twentieth-century embryologist who specialized in the development of amphibian embryos. A major emphasis of his research was refining the concept of the organizer, now referred to as

Eduard Friedrich Wilhelm Pflüger was a physiologist known for his research on respiration and the respiratory quotient, experiments on the effects of electricity on muscles and nerves, and his study of the ovaries and eggs development. His experiments on how the gravitational orientation of frog eggs affects their cleavage plane inspired embryologists such as

The scientific field of embryology experienced great growth in scope and direction in Germany from approximately 1850 to 1920. During this time, Adolf Ziegler and his son Friedrich crafted hundreds of