MAMMALIA 



403 



reduced to a single tusk in the upper jaw, which protrudes out in 

 front like a spear. This tusk is twisted in structure like a rawhide 

 ox-whip and is limited to the males, who use it in fencing contests 

 among themselves. 



Order 15. Mystacoceti (Whalebone Whales).— The whalebone 

 or baleen whales (Fig. 207, D) are the last word in adaptive specializa- 

 tion among mammals. The teeth are rudimentary and functionless, 

 present in the young but replaced in the adult by baleen. The nostrils 

 are paired; the skull is sjanmetrical ; the sternum is single; the ribs 

 are one headed, articulating only with the transverse processes of 

 the vertebra. The group is composed exclusively of large forais, 

 the only one that is less than a giant being the pigmy right whale, 

 which is only 

 about fifteen feet 

 in length. The 

 baleen or whale- 

 bone is a horny 

 material devel- 

 oped from the 

 epithelial lining 

 of the mouth 

 cavity. It is dis- 

 posed in curtain- 

 hke plates (Fig. 

 208), frayed out 



into fringes at the bottom. The plates reach a length of twelve or 

 more feet and are triangular, with the greatest width at the top or 

 attached end. As many as three hundred and seventy blades or 

 curtains, placed with their edges an inch or so apart, have been 

 counted in a single mouth. The function of the baleen is that of a 

 strainer. The great beast rushes through the water with the mouth 

 wide open, gathering in fishes or whatever else happens to be in the 

 way. Then the mouth closes and the water is forced out between 

 the sheets of baleen, while fishes, etc., are retained and swallowed. 

 Such huge creatures require vast quantities of food and cannot 

 become very numerous. Formerly whalebone was a commercial 

 product of some importance, used chiefly as stays in women's gar- 

 ments. Many substitutes, however, have been discovered and, more- 

 over, stays have gone out of fashion; so that the market value of the 



Fig. 208. — Skull of Baleen Whale, Balana mysticetus. 

 (From Weysse, after Glaus and Sodgwick.) 



