Letter, from Antoni van Leeuwenhoek to the Royal Society Printed copy sent instead of a signed autograph Investigating the structure of the muscle of the tongue of an ox and of a pig; investigating the heart of a sheep, ox, duck, chicken and cod Engraved figures are attached Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by a Committee of Dutch Scientists, vol 10, p 65 2 April 1694