They are known to dive deeper than one mile, and can stay down more than an hour. The important factor in avoiding the effects of pressure is that the lungs of deep-diving mammals are able to collapse completely. All the air is then compressed into the large air ducts and nasal passages, where no additional gas exchange takes place with the blood. Cetaceans have internalized their mammary glands and the nipples reside inside mammary slits, one on either side of the genital slit. The nipples are exposed by reflex when the calf nuzzles the mother.
Whale milk is much richer than cow's milk, and is about the consistency of cottage cheese.
Because the milk is so rich and thick, it can be squirted from the everted nipple of the mother into the mouth of the calf without much loss by dilution in the surrounding sea water. Whales, dolphins and porpoises all nurse their young this way. Whales and dolphins are thought to sleep with half the brain at a time, and are often observed, during quiescent periods, with just one eye open during these episodes. A resting whale breathes by reflex, bobbing slowly up and down in the water to take periodic breaths. Since the whale isn't moving much, it doesn't need to breathe very often as it rests.