1 The highest monthly average temperature in Keystone for July is 54 degrees. 2  The lowest monthly average temperature in Keystone for December is 14 degrees. 3  The most monthly precipitation in Keystone occurs in January with 0 inches.  The air quality index in Keystone is 15% better than the national average.
Simple eye in invertebrates. A simple eye (sometimes called a pigment pit) refers to a type of eye form or optical arrangement that contains a single lens. A simple eye is so called in distinction from a multi-lensed compound eye, and is not necessarily at all simple in the usual sense of the word. The eyes of humans and large animals, and camera lenses are classed as simple because in both cases a single lens collects and focuses light onto the retina or film.
Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of simple eye. compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual eye units), which are located on a convex surface, thus pointing in slightly different directions.