CLASSIFICATION AND CREATION 51 
no indication of radiate structure, but a super- 
ficial feature in no way related to the internal 
organization ; and therefore the Intestinal Worms 
must be removed from the branch of Radiates, 
and referred to that of Articulates. 
We must carefully distinguish between affinity 
and analogy among animals. The former is 
founded on identity of plan ; the latter only upon 
external resemblance. This may be produced by 
similar features, which, when intimately connected 
with the whole internal organization, as in some 
groups, may be considered as typical characters, 
but when only grafted, as it were, in a superficial 
manner on animals of another type, have no re- 
lation to the essential elements of structure, and 
become at once subordinate and unimportant. 
Such is the difference between the tentacles in a 
Radiate and the wreath of feelers in a Worm ; — 
the external effect may be much the same; but 
in the former every tentacle opens into one of 
the chambers, as in a Polyp, or connects with one 
of the radiating tubes, as in Acalephs, or with the 
locomotive suckers, as in Star-Fishes, and is there- 
fore closely linked with the whole internal or- 
ganization; whereas the feelers in the latter are 
only external appendages, in no way connected 
with the essential structural elements. We have 
a striking illustration of this superficial resem 
blance in the wings of Birds and Insects In 
