Linked from
The 18 pages that link to Antonie van Leeuwenhoek, each with the reason it gives.
MicroscopeRelated: His observations revealed living forms invisible to unaided sight.
CellRelated: His observations revealed living single-celled organisms invisible to the unaided eye.
GiardiasisRelated: He described Giardia-like organisms in his own stool in 1681.
DelftRelated: He was born and conducted much of his work in Delft.