定义：Description of the relationships among individuals within a population of organisms, including reproductive relationships (mating system), relationships within each sex, adult – young interactions, helpers and cooperation (group living).
定义：Solitary animals are those that spend a majority of their lives without others of their species, with possible exceptions for mating and raising their young. Antonyms for a solitary animal include a social animal or a colonial animal.
定义：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.
