16 THE NATURAL HISTORY OF THE COMMON CRAYFISH 
we put the Christian name, so to speak, after the sur- 
name. 
There are a number of kinds of Crayfish, so similar 
to one another that they bear the common surname of 
Astacus. One kind, by way of distinction, is called 
fluwiatile, another slender-handed, another Dauric, from 
the region in which it lives; and these double names are 
rendered by—Astacus fluviatilis, Astacus leptodactylus, 
and Astacus dauricus ; and thus we have a nomenclature 
which is exceedingly simple in principle, and free from 
confusion in practice. And I may add that, the less 
attention is paid to the original meaning of the sub- 
stantive and adjective terms of this bimomial nomen- 
clature, and the sooner they are used as proper names, 
the better. Very good reasons for using a term may 
exist when it is first invented, which lose their validity 
with the progress of knowledge. Thus Astacus fluviatilis 
was a significant name so long as we knew of only one 
kind of crayfish ; but now that we are acquainted with a 
number of kinds, all of which inhabit rivers, it is meaning- 
less. Nevertheless, as changing it would involve endless 
confusion, and the object of nomenclature is simply to 
have a definite name for a definite thing, nobody dreams 
of proposing to alter it. 
Having learned this much about the origin of the 
names of the crayfish, we may next proceed to consider 
those points which an observant Naturalist, who did not 
