Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed letter Duration of the life of spermotozoa 'in vitro'; dissecting the uterus of a bitch, killed after copulation, to investigate reproduction; stating that spermatozoa are the life-carriers and believes that there are male and female ones; observations of embryos in sheep; observations of ovaries in young animals; discussion of the embryo in the seed of an apple (expanded in EL/L1/76) Original figures now no longer exist with letter Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 5, p 139 English extract printed in 'Philosophical Transactions', vol 15, no 174, p 1120 30 March 1685