GRADATION OF FORM. 231 
structure: the chasms, indeed, remain vast; but 
there is no saltus, or leap, by nature, over one form 
to the other. 
(160.) Continuity, then, as applied to the ap- 
proximation or affinity of a series of animals, is not 
so expressive as the word gradation. And it is 
manifestly objectionable to employ, in science, the 
same term to express two very different meanings. 
After the preceding clear and able illustration by 
Mr. M‘Leay, we need only touch upon the nature 
of those intervals or chasms therein alluded to, and 
which, to a certain degree, are absolutely essential 
to that diversity of structure we meet with in nature. 
When these spaces between two objects are very 
small, as among the parrots, they create no idea in 
the mind of an hiatus, or a manifest inequality 
or interruption of gradation, sufficiently wide for 
the insertion of other forms. But, when they 
are great, as between the different types of the 
Pachydermata, then they assume the character of 
chasms, which might be filled up by numerous 
other forms, calculated to make the gradation from 
one to the other more easy. It might at first 
be supposed, indeed, that this inequality of gra- 
dation either implies the loss of many links in 
the series of pachydermatous quadrupeds, or a 
want of due harmony and equality in the con- 
struction of nature’s groups. A little reflection, 
however, on this apparent inconsistency will lead 
us to more correct conclusions. For this purpose 
we will still consider the Psittacide and the Pachy- 
dermata as striking examples of that inequality of 
gradation so frequent in different departments of 
Q 4 
