Chap. XIII. 
CLASSIFICATION. 
415 
they may be for tlie welfare of the being in relation to 
the outer world. Perhaps from this cause it has partly 
arisen, that almost all naturalists lay the greatest stress 
on resemblances in organs of high vital or physiological 
importance. No doubt this view of the classificatory im¬ 
portance of organs which are important is generally, but 
by no means always, true. But their importance for 
classification, I believe, depends on their greater con¬ 
stancy throughout large groups of species; and this 
constancy depends on such organs having generally been 
subjected to less change in the adaptation of the species 
to their conditions of life. That the mere physiological 
importance of an organ does not determine its classi¬ 
ficatory value, is almost shown by the one fact, that in 
allied groups, in which the same organ, as we have every 
reason to suppose, has nearly the same physiological 
value, its classificatory value is widely different. No 
naturalist can have worked at any group without being 
struck with this fact; and it has been fully acknow¬ 
ledged in the writings of almost every author. It 
will suffice to quote the highest authority, Eobert 
Brown, who in speaking of certain organs in the Pro- 
teacese, says their generic importance, like that of all 
their parts, not only in this but, as I apprehend, in 
every natural family, is very unequal, and in some cases 
seems to be entirely lost.” Again in another work he 
says, the genera of the Connaracese differ in having 
one or more ovaria, in the existence or absence of 
albumen, in the imbricate or valvular a3stivation. Any 
one of these characters singly is frequently of more than 
generic importance, though here even when all taken 
together they appear insufficient to separate Cnestis from 
Connarus.” To give an example amongst insects, in 
one great division of the Hymenoptera, the antennae, as 
Westwood has remarked, are most constant in structure; 
