The tiger is part of the kingdom Animalia, phylum Chordata, class Carnivora, family Felidae, subfamily Panthernae, genus/species Panthera tigris. Tigers have round pupils and yellow irises (except for the blue eyes of white tigers). Due to a retinal adaptation that reflects light back to the retina, the night vision of tigers is six times better than that of humans. Like domestic cats, tiger claws are retractable. Tiger scratches on trees serve as territorial markers. No one knows exactly why tigers are striped, but scientists think that the stripes act as camouflage (See diagram A), and help tigers hide