Nehemiah Grew wrote Letter L-066 of 1678-01-11 to Leeuwenhoek about comparisons of the size and shape of sperm from a variety of animals, the role of sperm in reproduction, and vessels in semen

There is no manuscript known.

In this letter, English botanist Nehemiah Grew passes along the greetings of Royal Society president Viscount Brouncker, who had asked Grew to write to L. Grew asks L. to compare the size and shape of sperm from a variety of animals. He contrasts the claims of William Harvey and Regnier de Graaf on the role of sperm in reproduction. Grew closes the letter by asking L. to further examine what he had reported as vessels in semen.

The present letter was published in Philosophical Transactions, vol. 12, p. 1043, directly after the excerpt from Leeuwenhoek’s Letter L-060 of November 1677 to Brouncker announcing his observations of sperm. It is followed by excerpts from Leeuwenhoek's next two letters, both to Grew, Letter L-070 of 18 March 1678, in which Leeuwenhoek responded to Grew’s letter in detail, and Letter L-073 of 31 May 1678, also about sperm. All three letters are in Collected Letters, vol. 2.