NUTRITION PROPER. 



305 



Mode of Feeding. — The baleen whales feed on 

 squids, cuttlefish, medusae, and small crustaceans, which 

 exist in enormous numbers in arctic seas, usually near 

 the surface. The whale rushes forward at great speed 

 with mouth open, so the water pours like a torrent into 

 the mouth and out at the sides between the plates. All 

 the surface animals are caught on the mossy roof and 

 sides. When a sufficient quantity is gathered the mouth 

 is closed, the superfluous water is spouted through the 

 blowhole (nostril), and the prey is swept up by the 

 tongue and swallowed. 



Homology of Baleen Plates. — These plates are a 

 substitute for, not a modification of, teeth. They are 

 therefore analogous, but not homologous with teeth. As 

 already explained, these 

 whales have rudiments 

 of teeth, which are nev- 

 er cut. What, then, are 

 the plates homologous 

 with ? They are prob- 

 ably extreme modifica- 

 tions of gum ridges — 

 such, e. g., as those found 

 on the mouth-roof of a 

 horse. If each of such 

 ridges produced a down- 

 ward growth of horny 

 tissue we should have 

 something like the ba- 

 leen plates of the whale. 



Birds. — Existing 

 birds have no teeth, yet 

 in the embryo of some 



birds rudimentary teeth are found which are never 

 developed. This is, of course, strong presumptive evi- 



FiG. ijt. — Ichtliyornis victor, x Jf. 

 (Restored by Marsh.) 



