TIIK DOCILE MAMMALS. 349 



metres (76 feet) in length. The largest of all whales, as of 

 all existing animals, is the fin-back (Fig. 248) or rorqual 

 (BalcBnoptera bnnps), which sometimes measures thirty-four 

 metres in length. The smallest Cetacea are the porpoises. 

 In the whalebone whales (Fig. 247) the teeth, present in 

 the embryo, become reabsorbed into the gums before birth 



FIG. 248. Fin-whale. 



and are replaced by plates of whalebone, three hundred of 

 which may be present on each side of the mouth. The in- 

 ner edges of these plates have projecting fibres, forming a 

 rude strainer; these whales feed on small pelagic jelly-fish, 

 mollusks, 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 



FIG. 5-19. Outline of the Cachelot, showing how the blubber is removed. l> the 

 situation of the "case;'' , the junk; (/, the bunch of the neck; /, the hump; ., 

 the ridge; k, the small; /, the tail or flukes; between the oblique dotted lines 

 are the spiral strips or blanket pieces. 



hundred pounds of whalebone have been obtained from a 

 single bow-head or Greenland whale (Balcena mysticetus). 



The cachelot or sperm-whale (Physeter macrocephalns, 

 Fig. 248) has an enormous head, and is without the power 

 of smell. In the upper jaw are cavities filled with a fatty 

 fluid called spermaceti, used in the manufacture of candles, 

 ointments, and cosmetics, such as cold cream. A large 



