a tiny fully formed individual that (according to the discredited theory of preformation) is supposed to be present in the sperm cell
Hippocrates and Aristotle proposed the idea of what they called pangenes, which they thought were tiny pieces of body parts. They thought that pangenes came together to make up the homunculus, a tiny pre-formed human that people thought grew into a baby. In the 1600s, the development of the microscope brought the discovery of eggs and sperm. Antonie van Leeuwenhoek, using a primitive microscope, thought he saw the homunculus curled up in a sperm cell. His followers believed that the homunculus was in the sperm, the father “planted his seed,” and the mother just incubated and nourished the homunculus so it grew into a baby. On the other hand, Regnier de Graaf and his followers thought that they saw the homunculus in the egg, and the presence of semen just somehow stimulated its growth. In the 1800s, a very novel, “radical” idea arose: both parents contribute to the new baby, but people (even Darwin, as he proposed his theory) still believed that these contributions were in the form of pangenes.
"my, that homunculus in your sperm really has your eyes!"