Letter, from Antoni van Leeuwenhoek to Nehemiah Grew, dated at Delft Signed autograph Observations of the sperm of dogs, rabbits, fish; discussion about fertilisation and the views of Regnier de Graaf and William Harvey about this; concerning the vessels in semen; observations of female reproductive organs; figures of spermatozoids are described as well as figures of the hair of a polecat Text refers to nine figures which are now no longer attached. Figures of the spermatozoids are reproduced in 'Philosophical Transactions', vol 12, no 142 EL/L1/35 for English translation Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 2, p 325 18 March 1678