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 

 fluviatile, another slender-handed, another Dauric, from 

 the region in which it lives ; and these double names are 

 rendered by — Astacus fluviatilis, Astacus leptodactylus,i 

 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 binomial 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 



