Translated extract of a letter, from Antoni van Leeuwenhoek to Hans Sloane Observations of a liver fluke; on the larvae of gnats; observations of a species of green algae belonging to the genus 'Volvox'; observations of circulation of blood in a frog and micro-organisms in its faeces Translated extract of EL/L3/13 English translation printed in 'Philosophical Transactions', vol 22, no 261, p 509 1700