216 FOOT-NOTES TO EVOLUTION. 
study, there we put our line of definition. ‘“ We can 
only predicate and define species at all,” says Dr. Coues, 
“from the mere circumstance of missing links. Species 
are the twigs of a tree separated from the parent stem. 
We name and arrange them arbitrarily, in default of 
means of reconstructing the whole tree in accordance 
with Nature’s ramifications.” * 
What is true of birds is equally the case with other 
groups of animals. Continued explorations bring to 
light each year new species of American fishes, but the 
number of new forms discovered each year is usually 
less than the number of old supposed species which are 
found to intergrade with each other, and have so become 
intenable. 
There is the closest possible analogy between the 
variations of species of animals or plants in different 
districts and that of words in different 
Beraleey De. languages. The language of any people 
tween variations . . . 
ei apedeoana 2° not a unit. It is made up of words 
words: which have at various times and under 
various conditions come into it from the 
speech of other people. The grammar of a language is 
an expression of the mutual relations of these words. 
The word as it exists in any one language represents the 
species. Its cognate or its ancestor in any other lan- 
guage is a related species. The words used in a given 
district at any one time constitute its philological fauna. 
* Dr, Allen says: ‘‘ We arbitrarily define a species as a group 
of individuals standing out distinct and disconnected from any 
similar group within which, though occupying different parts of 
the common habitat, we recognise other forms characteristic of 
and restricted to particular areas, These reach a maximum de- 
gree of differentiation at some point in the habitat, and thence 
gradually shade into other non-specific forms geographically con- 
tiguous.”—The Auk, January, 1890, p. 7. 
