Leeuwenhoek did not publish any letters after 1718 in book form with his own summaries. The summary below comes from Alle de Brieven / Collected Letters.
L. observes the reproductive organs of a ewe and a fetus from it. The observations made in September 1718 confirm that very early in the womb, the fetus is a very complete being, and not a shapeless mass.
Signed autograph letter. The manuscript is to be found in London, Royal Society, MS 2111, Early Letters L.4.79; 7 quarto pages; 1 engraving.
A contemporary English translation by Dr. Sprengell of the letter is to be found in London, Royal Society, Early Letters L.4.80; 5 pages.
The letter was read during the 8 November 1722 meeting of the Royal Society; Royal Society, Journal Book Original, vol. 13; Letter Book Original, 15.76.
The final part of the letter, after “I did these observations in the month of September 1718” was omitted when it was published in Philosophical Transactions.
Five figures came with this letter. L. did not send drawings, but a single engraving accompanied this letter. The figures 1-5 are to be found as Fig. I-V on the Plate with no. 373 of Philosophical Transactions.
This letter is written in the same hand as Letter 357 of 24 January 1721, in this volume. See the Remarks to that letter. The spelling and punctuation of both letters have the same characteristics. There are no periods at the end of sentences and no capital letters at the beginning. For the sake of readability, the translated text has been divided into full sentences, the punctuation has been modernized, and the paragraphing follows the text as printed in Philosophical Transactions.
