WHALES, PAST AND PRESENT. 



199 



ent in early stages of existence, which either disappear, or remain as 

 concealed and functionless organs, points to the present condition in 

 the aberrant and specialized forms as being one derived from the more 

 generalized type, in which the teeth were numerous and equal. 



Fig. 3. Toothed Whale, or Spermaceti Whale. 



The Mystacocetes, or whalebone whales, are distinguished by en- 

 tire absence of teeth, at all events after birth. But it is a remarkable 

 fact, first demonstrated by Geoffroy Saint-Hilaire, and since amply 

 confirmed by Cuvier, Eschricht, Julin, and others, that in the fetal 

 state they have numerous minute calcified teeth lying in the dental 

 groove of both upper and lower jaws. These attain their fullest 

 development about the middle of fetal life, after which period they 

 are absorbed, no trace of them remaining at the time of birth. Their 

 structure and mode of development have been shown to be exactly 

 those characteristic of ordinary mammalian teeth. It is not until after 

 the disappearance of these teeth that the baleen, or whalebone, makes 

 its appearance. This remarkable structure, though only a modification 

 of a part existing in all mammals, is, in its specially developed con- 

 dition as baleen, peculiar to one group of whales. 



Baleen consists of a series of flattened, horny plates, several hun- 

 dred in number, on each side of the palate, separated by a bare interval 

 along the middle line. They are placed transversely to the long axis 

 of the palate, with very short spaces between them. Each plate or blade 

 is somewhat triangular in form, with the base attached to the palate, 

 and the apex hanging downward. The outer edge of the blade is 

 hard and smooth, but the inner edge and apex fray out into long, 



