Microplate reader has measuring space, action source, measuring device for biological structure signals of microplate wells, transport support for positioning wells in relation to an optical axis of the device and controller for the action source, the measuring device and the transport support. An incubation apparatus with a frame accommodates a microplate with wells having bottoms for reducing liquid evaporation. The frame has a first opening surrounded by an inner wall for the microplate and an outer wall parallel to the inner wall and connected thereto by an intermediate bottom so that a channel is formed and the intermediate bottom for accommodating a liquid adjusted to the content of the microplate wells. The incubation apparatus has a support surface with a second opening for a microplate and, as a result, at least a portion of the well bottoms is freely accessible by the second opening.