OMNIVOROUS BIRDS AND PROTOCHORDATES 243 



RUNNING BIRDS (Ratit^) 



We next come to the Running Birds (Ratitae) of which the 

 African Ostrich [Struthio camelus) is almost proverbial for its 

 omnivorous habits. The general appearance of the bird is familiar 

 to all, and here attention need only be called to the broad short 

 beak and the wide gape. It is essentially a desert form, and is 

 often found associated with herds of antelopes. Its long neck is 

 of obvious advantage in enabling it to have a wide outlook. The 

 food in a wild state consists mainly of herbage, berries, and seeds, 

 but worms, insects, and the like, also small mammals, birds, and 

 reptiles, are by no means despised. The omnivorous habit appears 

 to be much increased in the case of captive specimens. Like all 

 birds in which the food requires crushing, it swallows small stones 

 and grit, as well as, it may be, other hard substances. 



The somewhat smaller South American Ostriches [Rhea) 

 closely resemble their African cousins in habit. The same is true 

 as regards the Emeus {Dromcsus) of Australia; but the Cassowaries 

 {Casuarius) of the Australian region are mainly vegetarian, and 

 live in forest regions. 



PRIMITIVE VERTEBRATES (Protochordata) 



There being nothing of special interest to detain us in the 

 great classes of Reptilia, Amphibia, and Fishes, the members of 

 which are predominatingly carnivorous, we come to the Proto- 

 CHORDATES, in which are included the simplest animals that have 

 any claim to be considered vertebrates. They are all omnivorous, 

 and exemplify two ways of feeding that are so typical for many 

 of the lower groups of animals that it will save a good deal of 

 repetition to describe them here in general terms. 



Sand and Mud Swallowers. — Marine sands and muds 

 contain a great deal of nutritive matter pardy of vegetable and 

 partly of animal origin. The same is true to a less extent of 

 similar freshwater deposits, and also as regards ordinary earth or 

 soil.' Many animals have become swallowers of such substances, 

 the object being to benefit by the nutritious substances therein 

 contained. 



Ciliary Currents. — The other mode of omnivorous feeding 

 to be noticed in this place is by means of cilia. These have 



