1854.] OF THE ROYAL INSTITUTION. 445 
and logical development of the doctrine,— have demonstrated the 
homology of all the parts of the Vertebrata, or in other words, that 
there is a common plan on which all those animals which possess 
back-bones are constructed, 
Precisely the same result has been arrived at, by the same methods, 
in another great division of the Animal Kingdom — the Annulosa. 
As an illustration, the Lecturer shewed how the parts of the mouth 
of all insects were modifications of the same elements, and briefly 
sketched the common plan of the Annulosa, as it may be deduced 
from the investigations of Savigny, Audouin, Milne-Edwards, and 
Newport. 
Leaving out of consideration (for want of time merely,) the Ra- 
diate animals, and passing to the remaining great division, the 
Mollusca,— it appears that the same great principle holds good even 
for these apparently unsymmetrical and irregular creatures: and the 
Lecturer, after referring to the demonstration of the common plan 
upon which those Mollusks possessing heads are constructed, — 
which he had already given in the Philosophical Transactions, 
— stated that he was now able to extend that plan to the remaining 
orders, and briefly explained in what way the ‘ Archetypal Mollusk’ 
is modified in the Lamellibranchs, Brachiopoda, Tunicata, and 
Polyzoa. 
We have then a common plan of the Vertebrata, of the Articulata, 
of the Mollusca, and of the Radiata,— and to come to the essence of 
the controversy in the Académie des Sciences — are all these com- 
mon plans identical or are they not? 
Now if we confine ourselves to the sole method which Cuvier 
admitted —the method of the insensible gradation of forms — 
there can be doubt that the Vertebrate, Annulose, and Molluscan 
plans are sharply and distinctly marked off from one another, by 
very definite characters; and the existence of any common plan, of 
which they are modifications, is a purely hypothetical assumption, 
and may or may not be true. But is there any other method of 
ascertaining a community of plan beside the method of Gradation ? 
The Lecturer here drew an illustration from Philology—a science 
which in determining the affinities of words also employs the 
method of gradation. Thus unus, uno, un, one, ein, are said to be 
modifications of the same word, because they pass gradually into one 
another. So Hemp, Hennep, Hanf, and Cannabis, Canapa, Chanvre— 
are respectively modifications of the same word: but suppose we 
wish to make out what, if any, affinity exists between Hemp and 
Cannabis —the method of gradations fails us. It is only by all 
sorts of arbitrary suppositions that one can be made to pass into 
the other. 
Nevertheless modern Philology demonstrates that the words are 
the same, by a reference to the independently ascertained laws of 
change and substitution for the letters of corresponding words, in the 
Indo-Germanic tongues: by shewing in fact, that though these 
