68 WHALEBONE AND WHALEBONE WHALES. 



overlaps them. By elevating its enormous fleshy tongue 

 within the cavity thus formed, the whale causes the 

 enclosed water to rush out between the plates, leaving such 

 small creatures as it contained lying high and dry on the 

 surface of the tongue ready for swallowing. 



In structure, whalebone (which, by the way, although 

 black in the Greenland whale, is white in some of the 

 other species) is of a horny nature, and grows from 

 transverse ridges on the mucous membrane of the roof of 

 the mouth ; being, in fact, nothing more than an ultra- 

 development of the ridges on the palate of a cow, hardened 

 and lengthened by an excessive growth of a horny super- 

 ficial or epithelial layer. The whole of this stupendous 

 horny growth takes place, however, after birth, young 

 whales having smooth palates, with no trace of the horny 

 plates. Although at birth young whalebone whales show 

 no traces of the substance from which the group derives 

 its name, they equally exhibit no evidence of the 

 presence of teeth. If, however, their jaws be examined at 

 a still earlier stage of development, it will be found that 

 there are a number of small teeth lying within a groove 

 beneath the gum on each side of both the upper and the 

 lower jaws. Previous to birth these teeth become absorbed, 

 and thus never cut the gum. Their presence in this 

 transitory stage is, however, of the deepest interest to 

 the evolutionist, since they unmistakably indicate the 

 derivation of the whalebone whales from ancestors 

 provided with a full series of functional teeth. This, 

 however, is not the whole of the story these rudi- 

 mentary structures have to tell. From the recent 

 investigations of Dr. Kiikenthal, it appears that in addition 

 to the above-mentioned tooth-germs, the jaws of very 

 young whales likewise exhibit traces of a still earlier 

 deciduous series of milk-teeth ; thus showing that the 

 former correspond to the permanent series of other 

 mammals. Accordingly, these tooth-germs do not represent 

 the functional teeth of the toothed whales, which, as we 

 have seen in the chapter on that group, correspond to the 

 milk-teeth of ordinary mammals. Even more remarkable 

 are certain observations relating to the structure of these 



