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 mammae 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 (Balcenoptera loops), 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 (Balwna mysticetus). 



