Swammerdam, Jan (1637–1680), a Dutch naturalist, often considered the founder of modern entomology (the study of insects). He also made valuable contributions to the knowledge of human anatomy. Swammerdam pioneered in the use of the microscope and dissection. He made detailed investigations of the anatomy and habits of insects and devised a system of classification based on the way their metamorphosis takes place. He demonstrated that when a muscle contracts its volume does not increase, discovered valves inside lymph vessels, and was probably the first to observe red blood cells (1658). Swammerdam was one of the first naturalists to oppose the theory of spontaneous generation. He was born in Amsterdam and studied medicine at the University of Leiden.