The term Class refers to a taxonomic level within the hierarchical system of classification between Phylum and Order. Organisms are included in this taxon based upon several methods of scientific scrutiny. One area is comparative morphology,which examines shapes and sizes of structures and their developmental origins. A second method is comparative biochemistry, which compares segments of amino acids in proteins and nucleotides in nucleic methods to distinguish groups. A third method is comparative cytology, which looks at changes in the number, shapes, and sizes of chromosomes and their constituents. Examples of classes include: Mammalia (mammals), Aves (birds), Reptilia (reptiles), Amphibia (amphibians), Osteichthyes (bony fish), Chondrichthyes (cartilaginous fish), Insecta (insects), Gastropoda (snails, slugs, and their relatives), Cestoda (tapeworms), Liliopsida (monocots), Magniliopsida (dicots), and many more.