The year 1691 in science and technology involved some significant events.
Biology
Italian Jesuit scholar Filippo Bonanni publishes the results of his microscopic observations of invertebrates in Observationes circa Viventia, quae in Rebus non-Viventibus.
Anton Nuck's Adenographia curiosa et uteri foeminei anatome nova is published at Leiden, including a description of the canal of Nuck[1] and a demonstration that the embryo is derived from the ovary and not the sperm.[2]