ORDERS OF MAMMALIA. 321 
size as compared with the body, and is rarely separable from the 
trunk by any distinct constriction or neck. There is no sacrum, 
and the pelvis is only represented in a rudimentary form. 
Lastly, the adult is either wholly destitute of teeth, or possesses 
only a single set, which are always conical in shape, and are 
never divisible into distinct groups. All the true Cefacea are 
carnivorous, living upon animal food. 
Chief amongst the Cetaceans in importance and zoological 
interest are the Whale-bone Whales (4a/enide), in which the 
adult is destitute of teeth, though the young whale possesses 
teeth which never cut the gum. The place of teeth is taken by 
a series of transverse plates of whale-bone or Ga/een, which are 
used as a kind of screening apparatus or filter to separate 
from the sea-water the minute Molluscs and Jelly-fishes upon 
which these enormous animals live. The most important 
member of this family, from a commercial point of view, is the 
Fig. 174.—Cetacea. The Common Dolphin (Delphinus delphis). 
Greenland Whale (Balena mysticetus), which yields most of 
the whale-oil and whale-bone of commerce. The Greenland 
Whale attains a length of from forty to sixty feet, and of this 
enormous length about a third is taken up by the head alone. 
The oil is derived from a thick layer of fat or “‘ blubber,” which 
is situated under the skin, and serves to protect them from cold. 
Though an inhabitant of the sea, the whale is obliged to come 
to the surface to breathe, and in so doing it ejects from the 
blow-holes what looks like a column of water, the whole opera- 
tion being known to the whalers as “ blowing.” The true nature 
of this act is still somewhat questionable, but it appears certain 
that the apparent jet of water is in reality, mainly if not entirely, 
due to the condensation of the moisture which is contained in 
the air expelled from the lungs. The old view was that “ blow- 
x 
