138 THE VITAL FUNCTIONS. 



lusca, and other small prey, by taking into its" 

 mouth the sea water which contains these ani- 

 mals, and allowing it to drain off through the 

 sides, after passing through the interstices of the 

 net work formed by the filaments of the whale- 

 bone. Some contrivance of this kind was even 

 necessary to this animal, because the entrance 

 into its oesophagus is too narrow to admit of the 

 passage of any prey of considerable size ; and it 

 is not furnished M'ith teeth to reduce the food 

 into smaller parts. The principal food of the 

 Balcena 3Iijsticetus, or great whalebone whale of 

 the Arctic Seas, is the small Clio Borealis, 

 which swarms in immense numbers in those 

 regions of the ocean ; and which has been al- 

 ready delineated in Fig. 120.* 



These remarkable organs for filtration entirely 

 supersede the use of ordinary teeth ; and ac- 

 cordingly no traces of teeth are to be discovered 

 either in the upper or lower jaw. Yet a ten- 

 dency to conform to the type of the mammalia 

 is manifested in the early conformation of the 

 whale ; for rudiments of teeth exist in the in- 

 terior of the lower jaw before birth, lodged in 

 deep sockets, and forming a row on each side. 

 The developement of these imperfect teeth pro- 

 ceeds no farther ; they even disappear at a very 

 early period, and the groove which contained 



* Vol. i. p. 258. 



