John Spangler Nicholas (March 10, 1895 – September 11, 1963) was an American embryologist and a professor of zoology at Yale University.
He contributed to experimental techniques for the study of embryology through transplants, the early stage development of teleost and mammalian zygotes.
Nicholas was born in Kintnersville, Pennsylvania, the only child of Reverend Samuel Trauger and Elizabeth Ellen.
Although the parents hoped he would join the Lutheran order, he chose to study medicine, influenced by an uncle, Harry Spangler.
Nicholas enlisted with the United States Army Medical Corps during World War I and returned following discharge in 1919.