In 1668 Francesco Redi, a famous Italian scientist, experimented with the spontaneous creation of maggots by placing the meat in two jars. His experiment disapproved of spontaneous generation as thought by Aristotle by he successfully demonstrated that maggots come from fly eggs. Antoni van Leeuwenhoek A Dutch microscopist was the first to invent the microscope. He observed the water and saw bacteria and protozoa. Prokaryotes are organisms made up of cells that lack cell nuclei, while eukaryotes possess a membrane-bound nucleus that holds genetic material.