He had an extraordinary range & skill of microscopic observations on the microscopic structure of the seeds and embryos of plants & small invertebrate animals. He discovered the existence of spermatozoa & of red blood cells and was thus founder of animal histology. Protozoa, algae, yeasts & bacteria -- all these unicellular organisms were first seen by Leeuwenhoek, often with such accuracy that it is possible to identify individual species from his accounts of them. This microbial world has two distinct features --- diversity and abundance.

Despite the simplicity of the microscopes made by Anton Van Leeuwenhoek, the highest magnification that he could obtain was consequently somewhat less than one third of the highest magnification that is obtainable with a modern compound light microscope. Leeuwenhoek constructed hundreds of such microscopes/instruments.

Leeuwenhoek

Anton Van Leeuwenhoek (1632 - 1723) observed the microbial world/the microscopic world only with the help of a simple microscope (microscope with one, almost spherical lens).