592 ZOOLOGY. 
limbs form a pair of paddle-like appendages just behind and 
under the head, which are supported by short, flattened 
limb-bones, the carpals and phalanges often separated by car- 
tilage ; the second digit being composed of more than three 
phalanges. There are two mamme situated near the anus. 
The external nostrils are either single or double, and are sit- 
uated on the top of the head ; they are modified to form the 
spiracles or ‘‘ blow-holes ;” certain folds of the skin prevent 
the water from entering the air-passages. The vapor blown 
from the holes does not consist of water, but of the mucus 
from the nostrils, and the moisture in the breath. The 
blow-holes vary in form in different kinds of whales. The 
“spout” of the sperm-whale issues in a single short 
stream from the extreme end of the snout, and curls over 
in front of the head; that of the fin-back whale forms 
a single column of vapor about ten feet high ; the right, 
humpback and sulphur-bottom whales each “blow” in a 
double stream which is directed backward toward the tail. 
Whales are rarely over fifty feet long; the sperm-whale 
has been known to reach a little over twenty-three metres 
(76 feet) in length, but Professor Flower questions whether 
the sperm-whale frequently, if ever, when measured in a 
straight line, exceeds a length of sixty feet. The largest of 
all whales, as of all existing animals, is the fin-back or ror- 
qual (Balenoptera boops), which sometimes measures thirty- 
four metres in length. The smallest Cetacea are the por- 
poises. 
In the Mysticete or whalebone whales, the teeth, present in 
the embryo, become reabsorbed into the gums before birth and 
are replaced by plates of whalebone (Fig. 514), three hun- 
dred of which may be present on each side of the mouth. 
The inner edges of these plates have projecting fibres, form- 
ing a rude strainer ; these whales feed on small pelagic jelly- 
fish, molluscs and crustacea, by taking in a mouthful of 
water, and then pressing the tongue against the roof of the 
mouth, expelling the water through the openings between 
the plates, the fibres acting as a strainer. Three thousand 
five hundred pounds of whalebone have been obtained from 
a single bow-head or Greenland whale (Balena mysticetus). 
