定義： Organic matter in soil which has reached a point of stability, where it will break down no further and might, if conditions do not change, remain essentially as it is for centuries, or millennia.
定義： A group of species that exploit the same food resources, and/or use the same feeding or foraging methods. http://en.wikipedia.org/wiki/Guild_(ecology)
定義： Because of the difference in refractive index between air and water (or corneal tissue), a curved cornea is an image-forming lens in its own right. Its focal length is determined by the radius of curvature of the cornea. Many corneal eyes (eg: in land vertebrates) also have lenses, but the lens is flattened and weakened compared with an aquatic lens; most of the refractive power is provided by the cornea. Corneal eyes cannot focus in aquatic habitat.
