Leeuwenhoek, Anton van (1632–1723), a Dutch biologist. Reconstructed greatly improved microscopes and became the first person to see bacteria and protozoans. In 1674 he gave the first accurate description of red blood corpuscles, and he later described the capillary action of the blood. Leeuwenhoek cast doubt on the theory of spontaneous generation by showing that grain weevils did not generate from decaying wheat, as was supposed, but from eggs deposited on the wheat. He discovered spermatozoa from his examinations of semen, and he was the first to observe that the aphid reproduces asexually, by parthenogenesis, as well as sexually.

Leeuwenhoek rarely left the town of Delft, where he was born and died. Although he had no academic training in science, he was elected a member of the Royal Society of London in 1680, and of the French Academy of Sciences in 1697.