MODIFICATIONS OF THE DIGESTIVE ORGANS. 7 



These examples, with those adduced in the first vohime, 

 will suffice to shew that great variations exist in the digestive 

 organs of birds, as well as in their external parts. Having 

 now examined those of more than four hundred species, I feel 

 qualified to say that in many cases the variations of structure 

 are rendered intelligible by connecting them with the known 

 habits of the birds, and that these organs are well adapted for 

 indicating affinities. Indeed, in most cases, one who has made 

 himself acquainted with their form and structure, as exhibited 

 in our most common birds, will be able with certainty, on 

 being shewn the interior of a bird, to announce the order to 

 which it physiologically belongs. 



Objections preferred against the use of anatomy, on the 

 ground of its being unnecessary for distinguishing species or 

 genera, or of its requiring more study than would be agreeable 

 to most people, are destroyed by the consideration of its utility 

 in characterizing families and other more comprehensive groups. 

 It is moreover absolutely childish to talk of external characters 

 as being sufficient indications of the nature of objects. A church, 

 or a theatre, or a warehouse, or a museum, may be distinguish- 

 ed from other buildings by its exterior ; but the construction 

 of its interior alone is what gives it its essential character. So 

 is it with a quadruped or a bird, of which the external parts 

 are but the envelopes of the organs, or appendages to them, as 

 essential however to the completion of the organization as the 

 most central parts. My dissections not being made for the 

 purpose of upholding a preconceived theory, or establishing an 

 arrangement founded on another basis, I may find it necessary, 

 in consequence of the gradual acquisition of knowledge, to alter 

 or modify the disposition or even the constitu^tion of the 

 groups which I have in the Introduction to the first volume 

 proposed for the Birds of Britain. Should this be the case, it 

 is hoped the reader will not consider me inconsistent, but al- 

 low me to apply tl^e same criticism to my own schemes that I 

 would employ in estimating those of another. Hitherto how- 

 ever, the five groups that have been described, namely the 

 Rasores, Gemitores, Deglubitores, and Cantatores, seem to be 

 perfectly natural, with this exception, that the two latter are 

 less distinct from each other than any of the rest. 



