Homunculus in a spermatozoon in a 1695 drawing and the first microscopic observations of sperm

This drawing of 1695 shows a spermatozoon. Inside the spermatozoon, in case you did not know, sits a little man, who makes his way into the womb and begins to grow until he becomes an infant. So, at any rate, the mathematician Nicolaas Hartsoeker saw it, peering at semen through a microscope. Such homunculi were dispelled only by researchers with more powerful microscopes.

The semen itself was first studied under a lens by the celebrated Antonie van Leeuwenhoek in 1677. At that time the presence of spermatozoa was explained by their being parasites inhabiting the "genital fluid".

The existence of the egg cell would be proved much later, in 1827.