There are millions of different types of living things on Earth. In order to keep track of them all, scientists put living things into groups based on characteristics that they have that are the same.

v. 1. Histological classification of bone and joint tumors of domestic animals / compiled and reviewed by M.V. Slayter [and others] -- v. 2. Histological classification of mesenchymal tumors of skin ...

This article discusses which animals deserve moral consideration, and whether some species are more deserving than others. The idea that non-human animals have significant moral status is ...