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 therefore closely linked with the whole internal
organization; 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 resemblance in the
wings of Birds and Insects. In Birds, wings are a typical feature,
corresponding to the front limbs in all Vertebrates, which are
constructed in the same way, whether they are arms as in Man, or
forelegs as in Quadrupeds, or pectoral fins as in Fishes, or wings as in
Birds. The wing in an Insect, on the contrary, is a flattened, dried-up
gill, having no structural relation whatever to the wing of a Bird. They
are analogous only because they resemble each other in function, being
in the same way subservient to flight; but as organs they are entirely
different.
In adding Infusoria to the Radiates, Cuvier was false to his own
principle of founding all classification on plan. He was influenced by
their seeming simplicity of structure, and placed them in the lowest
division of the Animal Kingdom on that account.
Pages:
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194