INTRODIJCTION. 
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Species is applied to the several animals of one kind; thus all the ducks, of one kind, constitute 
the species. This classification is founded upon similarity of color, size, proportion, form, &c. 
Variety is a term applied to animals which vary in some of their qualities from the general 
character of their kindred, while they are, in fact, of the same nature and structure. Genus is 
founded upon some of the less important characteristics of anatomy, such as the number and 
arrangement of the teeth, claws, fins, &c., and usually includes several species. Thus the lion, tiger, 
jaguar, puma, cat, &c., resemble each other in the qualities of their feet, teeth, and limbs, and 
therefore constitute a genus called /e/is. 
The term family is used to designate a group of several genera which have a resemblance to 
each other. Thus, the sprat, shad, herring, pilchard, and alewives, each forming a genus, con- 
stitute the family Clupeidce. The jays, jackdaws, crows, and ravens constitute the family Corvidce. 
Several of these families combined form an order, and several orders constitute a class, and classes 
form divisions. 
Another word of great use in natural history is type, which means the general idea of some animal 
which combines most fully the characteristics of the group to which it belongs. Thus the falcon 
may be selected as the type of the hawks, generally ; the duck may be taken as the ty^Q of the 
diving birds, generally ; and the mallard the type of the duck species. 
The knowledge of species constitutes the foundation of all zoological knowledge ; without this, 
we can never arrive at sound generalizations. The species, which forms the first step in classifi- 
cation, consists of an assemblage of individual animals which are supposed all to have descended 
from the same parents, and exhibit the closest possible resemblance in all parts of their structure. 
This definition, if definition it may be called, must not, however, be taken in the strictest sense 
which might be apj^lied to the words ; for in many cases we find that individuals undoubtedly 
belonging to the same species vary considerably among themselves, principally in color and size- 
Variation is generally to be observed, however, in animals under the influence of domestication;; 
the individuals of most species of wild animals resembling each other so closely that it would be 
difiicult to overlook their specific identity. 
A test for the specific identity of animals, upon which much stress has been laid, is founded 
upon the supposed fact, that when two animals of different species breed together, their' 
offspring, called hybrids, are barren. This test is evidently applicable only when we can have- 
the animals alive, subject to our notice ; while, even under the most favorable circumstances, 
such observations would be very inconclusive, as hybrids between undoubtedly distinct species 
have been frequently known to breed. 
MODEEN SYSTEMS OP CLASSIFICATION. 
The arrangement of the species of animals in genera, gives rise to the modern system of zoo- 
logical nomenclature. This is called the binomial system, from the circumstance that, according 
to this method, every animal receives two names, — one belonging to itself exclusively, the other 
in common with all the other species of the genus in which it is included. For example, the 
genus Felis, or cat, includes the lion, tiger, leopard, and cat, as species ; they all accordingly bear 
the generic name Felis, with the addition of a second name specially applied to each, serving to 
distinguish it from all other species of the genus : thus the lion is called Felis leo, the tiger Felis 
tigris, the leopard Felis leopardus, and the cat Felis catus. This method of nomenclature has 
at least this advantage over the plan of conferring only a single name upon each species — that 
when we hear for the first time the name of a newly discovered animal, if we are at all acquainted 
with the genus to which it belongs, the mere mention of the name puts us at once in possession of 
a considerable amount of inforination as to its structure, form, and habits. It was first adopted 
by the illustrious Linnaeus, the modern founder of Natural History, in the tenth edition of his 
" Systema Nature," published in 1*758. 
Proceeding with our ascending scale of classification, as indicated above, we find that the genera 
m their turn are sometimes united by common characters of importance into families, and these 
combine to form orders. In some cases we meet with intervening steps, uniting the tribes belonging 
to one order into two or three subordinate groups. The orders in their turn group themselves- 
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