Wrote Letter 28 of 1679-04-25 (AB 43) to Nehemiah Grew about living little animals in fish, hare, and dogs and his calculation that more than ten times as many living animals come from the milt of a cod as there are people living on the Earth

April 25, 1679
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Text of the letter in the original Dutch and in English translation from Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript on four folio pages, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1868. L 1. 40). Along with it is one page of calculations.


Leeuwenhoek published this figure in at least six different Dutch and Latin publications, all from the same plate. The one on the left sidebar is from the 1686 first edition of Levende Dierkens.

This figure of a dog's testicle is the only figure illustrating this letter. The original was drawn in red chalk by someone other than Leeuwenhoek: "I had a drawing made." He drew many of his own figures but did not have the technical skill for this one.

In the text, this figure had no label. It was so large that it appeared on a numbered page by itself in both the Dutch and the Latin editions. In later volumes, Leeuwenhoek would put such large figures on separately printed and unnumbered pages.

This letter was first published in Robert Hooke's Philosophical Collections, which made a different plate from the same drawing, still in the possession of the Royal Society. Few copies were printed and fewer preserved. The Google scan of this figure is not complete enough to include here.