SOME INTERNAL STRUCTURES 83 



distinctly analogous to the horny so-callecl teeth of 

 the Ornithorhynchus. And it is an interesting fact 

 that the whales show the same tendency observable in 

 other groups of the animal kingdom to the replace- 

 ment of teeth by horny structures. The horny teeth 

 of the Platypus have their forerunners in the shape 

 of true teeth, which are shed early. In birds the 

 most archaic forms had true teeth ; but the birds of 

 to-day have developed in their place the horny beak 

 which characterises them. 



The whalebone whales start life with rudimentary 

 teeth, which ultimately disappear on the appearance 

 of the whalebone. (See p. 68.) The general character 

 of whalebone resembles that of horns or hair. The 

 colour is black or white or brown. The place where 

 the whalebone is formed is the roof of the mouth, 

 the palate. The plates of whalebone are triangular 

 in shape, the base of attachment being broader than 

 the lower, free extremity. The plates are attached 

 by the broad base to the roof of the mouth, and they 

 may indeed be regarded as an exaggeration of the 

 ridges, often horny in character, which are found 

 upon the roof of the mouth of all mammals. The 

 plates are arranged in a direction transverse to the 

 long axis of the mouth and are very numerous, as 

 many as three hundred and seventy having been 

 counted. The blades are longest in the middle of 

 this long series, and gradually diminish towards both 

 ends of the mouth. The outside of the blades, that 

 turned towards the lips, is straight and hard ; the 

 inner side is frayed out into innumerable hair-like 

 processes. Thus an exceedingly efficient straining 



