The main techniques used are dissection and microscopy. Dissection is an ancient method used to find out the inside structure of a living thing (usually done after it is dead). It is still used by medical students to learn about the details of the human body. Simple microscopes were first invented in the 17th century, and the compound microscope (still used today) became available in the 19th century. The purpose of microscopy is to let us see the small details of structure. Also, the careful comparison of large collections of animals (usually in museums) is often done.