HOMOLOGIES. 903 
them, I would nevertheless attem})t to do it, in 
order to show how the countless forms of animal 
life have been generalized into the few grand, 
but simple intellectual conceptions on which all 
the past populations of the earth as well as the 
present creation are founded. In such attempts 
to divest the thought of its material expression, 
especially when that expression is multiplied in 
such thousand-fold variety of form and color, our 
familiarity with living animals is almost an obsta- 
cle to our success. For I shall hardly be able to 
allude to the formula of the Radiates, for in- 
stance, — the abstract idea that includes all the 
structural possibilities of that division of the An- 
imal Kingdom, — without recalling to my read- 
ers a Polyp or a Jelly-Fish, a Sea-Urchin or a 
Star-Fish. Neither can I present the structural 
elements of the Mollusk plan, without reminding 
them of an Oyster or a Clam, a Snail or a Cuttle- 
Fish, —or of the Articulate plan, without calling 
up at once the form of a Worm, a Lobster, or an 
Insect, —or of the Vertebrate plan, without 
giving it the special character of Fish, Reptile, 
Bird, or Mammal. Yet I insist that all living 
beings are but the different modes of expressing 
these formule, and that all animals have, within 
the limits of their own branch of the Animal 
Kingdom, the same structural elements, though 
each branch is entirely distinct. If this be true, 
