on the toes, the development of skin between the toes, are all points of structure which are variable.  The period at which the perfect plumage is acquired varies, as does the state of the down with which the nestling birds are clothed when hatched.  The shape and size of the eggs vary.  The manner of flight differs remarkably; as does in some breeds the voice and disposition.  Lastly, in certain breeds, the males and females have come to differ to a slight degree from each other.

Altogether at least a score of pigeons might be chosen, which if shown to an ornithologist, and he were told that they were wild birds, would certainly, I think, be ranked by him as well-defined species.  Moreover, I do not believe that any ornithologist would place the English carrier, the short-faced tumbler, the runt, the barb, pouter, and fantail in the same genus; more especially as in each of these breeds several truly-inherited sub-breeds, or species as he might have called them, could be shown him.

Great as the differences are between the breeds of pigeons, I am fully convinced that the common opinion of naturalists is correct, namely, that all have descended from the rock-pigeon (Columba livia), including under this term several geographical races or sub-species, which differ from each other in the most trifling respects.  As several of the reasons which have led me to this belief are in some degree applicable in other cases, I will here briefly give them.  If the several breeds are not varieties, and have not proceeded from the rock-pigeon, they must have descended from at least seven or eight aboriginal stocks; for it is impossible to make the present domestic breeds by the crossing of any lesser number:  how, for instance, could a pouter be produced by crossing two breeds unless one of the parent-stocks possessed the characteristic enormous crop?  The supposed aboriginal stocks must all have been rock-pigeons, that is, not breeding or willingly perching on trees.  But besides C. livia, with its geographical sub-species, only two or three other species of rock-pigeons are known; and these have not any of the characters of the domestic breeds.  Hence the supposed aboriginal stocks must either still exist in the countries where they were originally domesticated, and yet be unknown to ornithologists; and this, considering their size, habits, and remarkable characters, seems very improbable; or they must have become extinct in the wild state.  But birds breeding on precipices, and good fliers, are unlikely to be exterminated; and the common rock-pigeon, which has the same habits with the domestic breeds, has not been exterminated even on several of the smaller British islets, or on the shores of the Mediterranean.  Hence the supposed extermination of so many species having similar habits with the rock-pigeon seems to me a very rash assumption.  Moreover, the several above-named domesticated breeds have been transported to all parts of the world, and, therefore, some of