or birth. The vagina is long and wide. Genital passages are the oviducts of the cat. They are short, narrow, and not very sinuous. Male genitalia In the male cat, the genitalia includes two testicles and the penis, which is covered with small spines. Physiology Cats are familiar and easily kept animals, and their physiology has been particularly well studied; it generally resembles those of other carnivorous mammals, but displays several unusual features probably attributable to cats' descent from desert-dwelling species. Heat tolerance Cats are able to tolerate quite high temperatures: Humans generally start to feel uncomfortable when their skin temperature passes about , but cats show no discomfort until their skin reaches around , and can tolerate temperatures of up to if they have access to water. Temperature regulation Cats conserve heat by reducing the flow of blood to their skin and lose heat by evaporation through their mouths. Cats have minimal ability to sweat, with glands located primarily in their paw pads, and pant for heat relief only at very high temperatures (but may also pant when stressed). A cat's body temperature does not vary throughout the day; this is part of cats' general lack of circadian rhythms and may reflect their tendency to be active both during the day and at night. Water conservation Cats' feces are comparatively dry and their urine is highly concentrated, both of which are adaptations to allow cats to retain as much water as possible. Their kidneys are so efficient, they can survive on a diet consisting only of meat, with no additional water. They can tolerate high levels of salt only in combination with freshwater to prevent dehydration. Ability to swim While domestic cats are able to swim, they are generally reluctant to enter water as it quickly leads to exhaustion. See also Cat senses Natural bobtail References External links The cat; an introduction to the study of backboned animals, especially mammals (1881) A laboratory guide for the dissection of the cat: An introduction to the study of anatomy (1895) Anatomy of the cat (1902) Felinology Felidae anatomy