PORPOISES, DOLPHINS, AND WHALES 29 



long, and possesses something like thirty-two sharp conical teeth, 

 curved slightly backwards. Those near the front of the beak are 

 larger than the others. 



Sperm -Whale Family {Physeteridce). — The largest species 

 here is the gigantic Sperm- Whale or Cachalot {Physeter macro- 

 cephalus), that rivals in size the toothless whales, attaining as it 

 does a length of 90 feet, of which about one -third is taken up 

 by the huge squarish head. No traces of teeth are to be seen in 

 the upper jaw of the adult, but at an early period of existence 

 vestiges of them are found in the substance of the gum, though 

 not visible externally. The lower jaw is armed with numerous 

 (twenty to twenty-five each side) massive conical teeth, which fit 

 into pits in the upper jaw. The food is said to consist entirely 

 of squids and cuttle-fishes, and huge specimens of the sort are 

 probably more numerous in the open sea than is generally 

 imagined. 



TOOTHLESS OR WHALEBONE WHALES (Mystacoceti) 



This sub-order includes the largest animals now existing on 

 the earth, sperm-whales alone excepted. The longest of them (up 

 to 115 feet) is the Rorqual of the North Atlantic {Balcenoptera 

 boops), but the most familiar species is the Right or Greenland 

 Whale {Balcena mysticetus), which, though not so long (80 feet), 

 is much more bulky, and may attain a weight of almost 1 50 tons. 

 At a very early stage in its existence teeth begin to form in the 

 jaws of this animal (as indeed in the toothless forms generally), 

 but they never cut the gum, and later on all trace of them is lost. 

 No doubt the ancestral forms from which these whales are de- 

 scended possessed numerous teeth resembling those of dolphins 

 and porpoises, and these useless vestiges are reminiscent of the 

 toothed stage in the history of the sub-order. They afford one 

 of the most striking instances known of the Law of Recapitula- 

 tion, in accordance with which the development of the individual 

 presents an imperfect epitome of the evolution of the species. 

 It is one of the most extraordinary facts in the whole of zoology 

 that these enormous toothless creatures mainly depend upon very 

 minute animals as food. Floating upon the surface of the ocean 

 are vast assemblages (known as " plankton ") of small molluscs, 

 crustaceans, '&c., and it is these which are the chief diet of the 



