Jean Clark Dan came to MBL in 1931 as an undergraduate in the Invertebrate Zoology Course. She spent summers here until 1936, when she completed her PhD with Victor Heilbrunn at the University of Pennsylvania. After marrying in 1937, Jean and Katsuma Dan moved to Japan and continued research at the Misaki Marine Station.

Jean Clark Dan returned to MBL in 1947 and met Ken Cooper, who persuaded Edwin Grant Conklin to arrange a grant from the American Philosophical Society for a phase contrast microscope for the Misaki Marine Station. Phase contrast microscopes can reveal cellular structures not seen with bright field microscopy and allows experimentation with living cells.

Jean Dan at her desk in 1932
Dans working
Jean Clark Dan and Katsuma Dan (Woods Hole Historical Museum)

Jean Clark Dan characterized the acrosomal reaction in sea urchins, a crucial step in penetration of the egg by sperm during fertilization.

1. Still Image: "Jean Clark Dan", 6/11/2012,

2. Jean Clark Dan and Katsuma Dan in their laboratory at the Misaki Marine Biological Station.
Credit: Dr. Mariko Kondo, MMBS. Photo courtesy of the Woods Hole Historical Museum.

3. Dan, Jean C. 1950. “Sperm Entrance in Echinoderms, Observed with the Phase Contrast Microscope.” The Biological Bulletin 99(3): 399–411. 

4. Dan, Jean C. 1952. “Studies on the Acrosome. I. Reaction to Egg-Water and Other Stimuli.” The Biological Bulletin 103(1): 54–66. 

5. Colwin, Laura Hunter and Colwin, Arthur L. 1979. "Obituary: Jean Clark Dan." Nature 278: 492.