WHAT CONSTITUTES A SPECIES f 
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and changing the character of species, yet it will thus 
appear the union of different sexes tends to produce 
variation in either of the two hereditary lines united. 
There is no better place than this to present an ex¬ 
planation of the meaning of species. 
WHAT CONSTITUTES A SPECIES? 
For convenience of reference and study, scientists 
have classified both animals and plants into species, 
genera, families, orders, and classes. Mr. Huxley 
says; “ A species is the smallest group to which dis¬ 
tinctive and invariable characteristics can be assigned.” 
Species are based upon form and structure, both 
external and internal. Animals of the same species 
must be able to produce beings like themselves, which 
shall again produce their kind. Animals of the same 
species are supposed to vary from each other only 
in color and proportions. Such variations would be 
called varieties of the species. 
A genus includes one or more species. For in¬ 
stance, the foxes belong to the genus Yulpes. Wolves 
and dogs each belong to a different genus. In de¬ 
scription two names are used: genus and species. 
The genus is written first, and usually begins with a 
capital letter. Thus the common fox of Europe is 
known as Yulpes vulgaris ; the arctic fox is the H. 
lagopus ; and our common red fox, Y. fvlvus, is really 
only a variety of the Y. vulga/ris, and may properly 
be called a subspecies. The cross and silver foxes 
again are color varieties of the red. 
