HUMP-BACKED WHALE (PLACENTAL)
The subclass Eutheria includes a vast group of diverse species such as primates (monkeys, apes, humans); insectivores (shrews, moles, hedgehogs, tenrecs); cetaceans (whales, porpoises, dolphins); carnivores (lions, tigers, wolves); and many other orders of mammals.

Eutheria species are placental, meaning the young develop in the womb of the mother while attached to a placenta. Through the placenta, nutrients pass from the mother to embryo, and wastes travel from embryo to mother.

Cetaceans such as whales, including the humpback whale, are adapted to live, breed, rest, and carry out all of their life functions in the water.

Among the features many cetaceans use to survive are:

• A streamlined body shape
• Paddle-shaped front limbs
• A hairless body (though some young have hair on their snouts)
• A lack of sweat glands
• Internal reproductive organs
• Small or hidden ears and hind limbs
• A thick subcutaneous blubber layer filled with fat and oil

Many of these features help reduce drag for efficient swimming. This is especially important for whales traveling thousands of kilometers during migration. Body-part extensions such as external ears or genitals would increase drag.