Letter, from Antoni van Leeuwenhoek to Robert Hooke, dated at Delft Signed autograph Observations of the testicles and spermatozoids of a rat; hopes to examine the semen of mussels; observations of organisms in the gills of oysters; observations of organisms in the sap of vines Two ink figures: one of sperm and one of a testicle of a rat in a jar of water EL/H3/73 for Robert Hooke's partial translation Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 3, p 201 English extract printed in 'Philosophical Transactions', vol 17, no 196, p 593 5 April 1680