THE FIVE GEEAT BRANCHES. 21 



All birds which are specially fitted by their structure and 

 form for capturing other birds and quadrupeds for food, 

 constitute one Order, called the Raptores or Birds of Prey ; 



All birds of prey which have the head covered with 

 feathers, and the eyes on the sides of the head, and more or 

 less sunken, constitute one Family, called the Falconidse ; 



All of the members of the Falcon Family which have the 

 bill short, and strongly curved from the base to the tip, 

 and which have a distinct horny tooth in each side of the 

 upper mandible, constitute one Genus, the true Falcons ; 



All the members of the genus of Falcons, which are 

 essentially like our common Duck Hawk (Falco anatuni), 

 constitute one Species ; all that are essentially like our 

 common Sparrow Hawk (Falco sparverius), constitute 

 another species; and so on.* 



Other Branches, Classes, Orders, etc., of the Animal 

 Kingdom are formed in a similar manner. 



Cuvier recognized four great Brandies or Types in the 

 Animal Kingdom the Yertebrata, the Articulata, the 

 Mollusca, and the Radiata. Most or at least, many nat- 

 uralists of the present day recognize, in addition to these, 

 a fifth group, called the Protozoa, including a vast num- 

 ber of small, minute, and microscopic organisms, together 



* The question, "What is a species ? " has never been answered to the en- 

 tire satisfaction of all naturalists. But practically we may refer to a given 

 species all those individuals that are essentially alike ; so essentially alike 

 that there is sufficient evidence for believing that they have descended from 

 one pair or a common ancestry. 



The doctrine held by many distinguished naturalists that in a certain 

 sense all animals hawe had a common origin, that is, that our present "spe- 

 cies " have been evolved from other and earlier species, and the latter from 

 still earlier species, and that in the beginning of life on the globe there were 

 only a few simple forms, and probably only one simple form cannot be 

 dwelt upon here. For the views of these naturalists, as to the " Origin of 

 Species," and as to the doctrine of " Evolution," see the writings of Darwin, 

 Huxley, Mivart, Cope, Hyatt, Gill, and others. 



