THE COLUMBID.E. 
61 
opportunities of gaining- information which are not easily recovered. It is only as 
the mind becomes familiar with one subject, that it is prepared to see the different 
bearings of those that are related to it, and to appropriate them to its use. When 
I commenced the pursuit, I had read nothing whatever on the subject, and had 
no one to direct my labour. I was not even aware, that some birds had c»ca and 
others none, that the sclerotic membrane of their eye was furnished with, and 
supported by, a ring of bony plates, or any other of the facts of comparative 
anatomy. But to return, 
I now come to the points of agreement between the Rasores and the CoiumMdts, 
Here I find myself quite at fault, and shall be glad of the friendly assistance of 
my readers; - for I find a total absence of that kind of resemblance, either in habit, 
function, form, or internal structure, which I think ought invariably to accompany 
the different families of one order. Indeed the only points of similarity I can 
discover betweeen them, are, that the one is principally and the other entirely a 
vegetable feeder; and that they each have a membranous crop as well as‘ a carti¬ 
laginous one, and a gizzard; even these are shared by several other families 
of birds, and the membranous crop of the- Rasores and the Columbidm differs in 
shape; in the former it is globular, in the latter composed of two lobes. 
Pmonidm and TetrmnidcB are said by Selby to constitute the typical forms 
of the Rasores ; Craeidm^ Struthionidas^ and Columbidee^ to be aberrant families of 
the same group. To shew in how unequal a degree they are entitled to the term 
aberrant, I would observe, that out of 17 distinct points of agreement existing 
between the Pavonidm and the Tetraonid^e^ the Crucidse agree with them 
in fourteen, the Struthionidae in seven, and the Columbidm in only one. 
To make the order Rasores consist of these five families, appears to me very 
incongruous, and to arise more from a desire of adapting them to the exigences of 
a preconceived theory, than from any natural affinities observable between them. 
A circle* composed of families differing so greatly in the amount of their aberra¬ 
tions, presents, according to my ideas, chasms so extensive and frightful between 
the different families of which it is composed, as not at all to accord with the 
beautiful order of Nature; whereas, if placed in separate orders, we find the ex¬ 
treme species running into each other, and forming one harmonious whole, which 
cannot be contemplated without feelings of admiration and delight. 
* I ha¥e written the preceding observations without being aware of the views of the Editor of 
The NatumUst on Systematic Zoology, and of course without wishing to hurt the feelings of any 
one. I have, in fact, given my own candid opinion on the subject.—-T, A.——[This is precisely 
what we should wish all our Correspondents to do. Although we would by no means have our 
readers suppose that Mr. Allis has, in the above paper, demolished the quinary or circular 
theory, yet we consider his remarks well worth the attention of the quinary systematist.— Ed.] 
