During the late 1880s and early 1890s, Wilson turned his attention primarily to cell lineage studies of early-stage embryos. The purpose of this work was to follow each individual cell in the embryo from the very first division of the fertilized egg onwards in hopes that doing so might shed light on the specification of cell and tissue fates. This approach to studying embryology both demonstrated and reinforced the idea that individual cells and their division play an important role in early development.
The culmination of Wilson’s cell lineage work, particularly his studies of the polychaete worm Nereis limbata at the MBL, was his 1892 publication The Cell-Lineage of Nereis: a Contribution to the Cytogeny of the Annelid Body. This comprehensive, one hundred page paper was accompanied by eight lithographic plates depicting ninety-two carefully illustrated figures. Given that this work required extremely close observation of individual cell movements, Wilson relied heavily on drawings and sketches both to carry out and effectively present his work.