River otters primarily eat fish. They are also known to eat whatever is easiest to find, like crustaceans, mollusks, insects, birds, oysters, shellfish, crabs, crayfish, frogs, rodents, turtles and aquatic invertebrates.
1667: Robert Hooke 's famous Micrographia is published, which outlines Hooke's various studies using the microscope. 1675: Enter Anton van Leeuwenhoek, who used a microscope with one lens to observe insects and other specimen. Leeuwenhoek was the first to observe bacteria. 18th century: As technology improved, microscopy became more popular among scientists. Part of this was due to the discovery that combining two types of glass reduced the chromatic effect.
It is difficult to say who invented the compound microscope. Dutch spectacle-makers Hans Janssen and his son Zacharias Janssen are often said to have invented the first compound microscope in 1590, but this was a declaration made by Zacharias Janssen himself during the mid 1600s. The date is unlikely, as it has been shown that Zacharias Janssen actually was born around 1590.