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.
Some cells are visible to the unaided eye. The smallest objects that the unaided human eye can see are about 0.1 mm long. That means that under the right conditions, you might be able to see an ameoba proteus, a human egg, and a paramecium without using magnification. A magnifying glass can help you to see them more clearly, but they will still look tiny.