Chap. XIII. 
CLASSIFICATION. 
427 
stances: thus Linnaeus, misled by external appearances, 
actually classed an homopterous insect as a moth. We 
see something of the same kind even in our domestic 
varieties, as in the thickened stems of the common and 
Swedish turnip. The resemblance of the greyhound and 
racehorse is hardly more fanciful than the analogies 
which have been drawn by some authors between very 
distinct animals. On my view of characters being of 
real importance for classification, only in so far as they 
reveal descent, we can clearly understand why analogical 
or adaptive character, although of the utmost importance 
to the welfare of the being, are almost valueless to the 
systematist. For animals, belonging to two most distinct 
lines of descent, may readily become adapted to similar 
conditions, and thus assume a close external resem¬ 
blance ; but such resemblances will not reveal—will 
rather tend to conceal their blood-relationship to their 
proper lines of descent. We can also understand the 
apparent paradox, that the very same characters are 
analogical when one class or order is compared with 
another, but give true affinities when the members of 
the same class or order are compared one with another: 
thus the shape of the body and fin-like limbs are only 
analogical Avhen whales are compared with fishes, being 
adaptations in both classes for swimming through the 
water; but the shape of the body and fin-like limbs 
serve as characters exhibiting true affinity between the 
several members of the whale family; for these ceta¬ 
ceans agree in so many characters, great and small, 
that we cannot doubt that they have inherited their 
general shape of body and structure of limbs from a 
common ancestor. So it is with fishes. 
As members of distinct classes have often been 
adapted by successive slight modifications to live under 
nearly similar circumstances,—to inhabit for instance 
