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 

 Pacliydermata* 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 Psittacida and the Pachy- 

 dermata as striking examples of that inequality of 

 gradation so frequent in different departments of 

 q 4 



