112 ELEMENTS OF COMPARATIVE ZOOLOGY. 



According to the presence or absence of teeth the living 

 whales are divided into two groups. In some of the .toothed 

 whales but two teeth are present ; others may have a large 

 number ; and usually these cannot be well distributed 

 among incisors, canines, etc., as all are essentially alike in 

 size and shape. In the male narwal, however, one of the 

 upper teeth on one side (apparently a canine) grows straight 

 forward into a long twisted spear eight or nine feet in 

 length, while the other teeth disappear at an early age. 

 The killer-whales are comparatively small, but are among 

 the most voracious of mammals, not hesitating to attack 

 the largest whales. Here also belong the blackfish, por- 

 poises, and dolphins. The sperm-whales are larger, and 

 have no teeth in the upper jaw, while the lower jaw is abun- 

 dantly supplied. They derive their common name from the 

 spermaceti which they produce. This is a solid granular 

 substance found in the "case," a cavity occurring on the 

 right side of the front of the head between the skin and the 

 skull. 



The toothless whales are also known as whalebone whales, 

 from the fact that they bear 

 upon the lower sides of the 

 upper jaw hundreds of long par- 

 allel plates of so-called whalebone 

 or baleen. These plates are 

 fringed at the end, and the whole 

 apparatus forms an efficient 

 strainer, used in separating the 



FIG. 46 Section through the ,, , -. . -. ,-, 



head of a whalebone whale Small animals Upon Which these 



(after Boas), showing how the , , _ , ,-, -. 



plates of baleen (w) are ar- whales feed from the surround. 



ranged on either side of the . T , . , , 



mouth-cavity (m) The true ing water. It is among these 



bones are shown black. 111 i_ i 1 1 i 1-1 



whalebone whales that the giants 



among mammals occur. The right whales of the Arctic 



