MOUTH OF THE WHALE. 103 



water. , Thus, the whale is enabled to collect a whole shoal 

 of mollusca, and other small prey, by taking into its mouth 

 the sea water which contains these animals, and allowing it 

 to drain off through the sides, after passing through the in- 

 terstices of the net work formed by the filaments of the 

 whalebone. Some contrivance of this kind was even neces- 

 sary to this animal, because the entrance into its oesophagus 

 is too narrow to admit of the passage of any prey of consi- 

 derable size; arid it is not furnished with teeth to reduce the 

 food into smaller parts. The principal food of the Balana 

 Mysticetus, or orreat whalebone whale of the Arctic Seas, is 

 the small Clio Borealis, which swarms in immense num- 

 bers 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, accordingly, no traces of 

 teeth are to be discovered either in the upper or lower jaw*. 

 Yet a tendency to conform to the type of the mammalia is' 

 manifested in the early conformation of the whale; for rudi- 

 ments of teeth exist in the interior of the lower jaw before 

 birth, lodged in deep sockets, and forming a row on each 

 side. The development of these imperfect teeth proceeds 

 no farther; they even disappear at a very early period, and 

 the groove which contained them closes over, and, after a 

 short time, can no longer be seen. For the discovery of 

 this curious fact we are indebted to Geoffroy St. Hilaire.t 

 In connexion \fith this subject, an analogous fact, which has 

 been noticed in the parrot, may here be mentioned. The 

 young of the parrot, while still in the egg. presents a row of 

 tubercles along the edge of the jaw, in external appearance 

 exactly resembling the rudiments of teeth, but without being 

 implanted into regular sockets in the maxillary bones: they 

 are formed, however, by a process precisely similar to that 

 of dentition; that is, by deposition from a vascular pulp, 

 connected with the jaw. These tubercles are afterwards 



* Vol. i. p. 186. 



f Cuvier, Ossemens Fossiles, 3me edition, torn. v. p. 360. 



