228 COMPARATIVE ZOOLOGY. 
dom, which includes all animals formed upon one of the 
four or five types of structure; as Vertebrate. 
These terms were invented by Linnzeus, except Family 
and Subkingdom, which were added by Lamarck. To Lin- 
nus we are also indebted for a scientific method of nam- 
ing animals. Thus, a Dog in Zoology is called Canis 
Jamiliaris, which is the union of a generic and specific 
name, corresponding to the surname and Christian name 
in George Washington, only the specific name comes last. 
It will be understood that these are abstract terms, ex- 
pressing simply the relations of resemblance: there is no 
such thing as genus or species. 
Classification is a process of comparison. He is the best 
naturalist who most readily and correctly recognizes like- 
ness founded on structural characters. As it is easier to 
detect differences than resemblances, it is much easier to 
distinguish the class to which an animal belongs than the 
genus, and the genus than the species. In passing from 
species to classes, the characters of agreement become few- 
er and fewer, while the distinctions are more and more 
manifest; so that animals of the same class are more like 
than unlike, while members of distinct classes are more 
unlike than like. 
To illustrate the method of zoological analysis by search- 
ing for affinities and differences, we will take an example 
suggested by Professor Agassiz. Suppose we see together 
a Dog, a Cat, a Bear, a Horse, a Cow, and a Deer. The 
first feature which strikes us as common to any two of 
them is the horn in the Cow and Deer. But how shall 
we associate either of the others with these? We examine 
the teeth, and find those of the Dog, the Cat, and the Bear 
sharp and cutting; while those of the Cow, the Deer, and 
the Horse have flat surfaces, adapted to grinding and 
chewing, rather than cutting and tearing. We compare 
these features of their structure with the habits of these 
