196 Mammals of Eastern Asia 
the hind limbs are obsolete or represented by rudiments within 
the body; the tail is broadened horizontally into a transverse fin 
used for propulsion and for directing the body up or down in 
the water. The forelimbs are used in balancing and turning, as 
well as to help drive the Whale through waters. In most Whales 
the skull and neck bones are compressed and telescoped, thus 
eliminating the narrowing at the neck and providing the famihai 
torpedo-shaped outline. The eyes are much reduced for the size 
of the animals and the ears externally are obsolete. Breathing 
takes place in the Whalebone Whales through a double blow- 
hole; a single blow-hole, which can be closed before the Whale 
submerges and which is formed by the internal union of the two 
"nostrils/' is found in the Toothed Whales. One of the internal 
air passages in certain kinds of Toothed Whales may be en- 
larged at the expense of the other. This internal asymmetry, 
coupled with special air sacs developed on one side only, is indi- 
cated externally by the blow-hole being off center. 
Marine Whales normally come to the surface to breathe with 
frequencies dependent upon the species. Howell gives eight to 
twelve minutes for the Humpback, twelve to fifteen for the 
Bowhead, but thirty to sixty minutes for the Sperm Whale. 
River Porpoises probably surface much more frequently. 
Whales produce one calf at a time. Being truly mammals, they 
give milk; the single pair of nipples is situated near the vent. 
In the past, whaling has been a very important industry. Re- 
lentless hunting of Whales for the oil contained in their bodies, 
for the "whalebone" of the Whalebone Whales, and more re- 
cently for their flesh, to be made into fertilizer or even to be 
canned, has so greatly reduced their numbers that certain species 
are verging on extinction. Formerly they were killed with hand- 
thrown harpoons, later with harpoons shot from guns. More 
recently they have been slaughtered by the use of harpoons 
carrying electrical charges that are conducted through the cables 
attaching them to ships. But perhaps the most efficacious death- 
