Letter, from Antoni van Leeuwenhoek to Nehemiah Grew, dated at Delft Signed autograph Observations of the sperm of cod, pike, birds; observations of the testicles and sperm of a hare and of a dog; calculations for determining the number of sperms in the milt of a cod Diagram of the testicle of a dog in red chalk is attached Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 3, p 3 25 April 1679