520 MANUAL OF ELEMENTARY ZOOLOGY 



Order Ungulata. 



Sub-order Artiodactyla. 

 Tribe Suina. 

 Tribe Ruminantia. 



Sub-order Perissodactyla. 



Sub-order Proboscidea. 



Sub-order Hyracoidea. 

 Order Rodentia. 

 Order Carnivora. 

 Order Insectivora. 

 Order Chiroptera. 

 Order Primates. 



Sub-orders : Lemuroidea, Anthropoidea. 



The discovery of differences such as those with which we 



have just been concerned is one of the main 

 The Meaning tasks of zoology, but it is not the whole task. 

 between 8 " 088 As we saw la the first chapter, an essential 

 Animals. part of the science is the attempt to explain 



the differences which it finds. The unlikeness 

 between the several kinds of animals is not explained by 

 the fact that in most, if not in all, cases it corresponds to 

 differences in their lives. A full explanation of it can only 

 be reached when we know both how it has arisen and why 

 it is connected with different modes of life. 



From the earliest days of the science two theories have 



been current as to the origin of the differences 

 "Proofs?" between the several kinds of animals. One 



contents itself with the statement that each 

 species has come into being independently by a process of 

 special creation, whose method it does not attempt to 

 explain. The other alleges that every species has sprung 

 from some other species that was in existence before it, by 

 a process known as evolution, which arises from the exist- 

 ence of differences between parents and their offspring, 

 and that the differences upon which the zoologist founds 

 genera and higher groups are due to the unlikeness between 

 species being increased by the same process. Evolution is 

 an alteration of the average characters, either of the whole 

 of a species or of a certain group of its members, from 

 generation to generation in a constant manner, by which 

 they become so different from what they were at first 

 that a new species arises. This theory is now held by 

 all zoologists. It is based upon several classes of evidence. 



