NATURAL SELECTION. 
157 
same time by retrograding metamorphoses, as seen in 
parasites, etc. 
While Natural Selection is generally admitted to be a 
sufficient cause for the production of unimportant variations, 
it is often objected that important structures, such as the 
skeleton, could never be modified by such a process. Mr. 
Darwin, however, has shown that the skeleton is as sus- 
ceptible to modification as any other part of the organization. 
— 
Thus, the different kinds of pigeons, supposed unanimously 
by “fanciers” to have descended from different ancestors, 
but which are now known to be the posterity of the Rock 
Pigeon, offer great variations in their skeleton, as in the 
number of their vertebrae and ribs, in the character of the 
breast-bone, merry-thought, lower jaw, and bones of the 
face. All zoologists admit that the various kinds of rabbits 
have descended from a common stock ; and yet the greatest 
difference is seen in the size, shape, and form of the skull, 
in the character of the backbone, etc. But not only have 
the changing of conditions and the.domestication of animals 
modified the skeleton, which is regarded by anatomists as 
one of the most constant of characters, but the viscera and 
all other parts of the organization have been affected. We 
do not regard, therefore, the objection of Natural Selection 
not being a sufficient cause of change as of any weight. 
The fact of Hybrids often not breeding is regarded by 
many as an important objection. The case of the mule not 
breeding is usually referred to. This objection does not 
seem to us to amount to much, as it is well known that the 
Porto Santo rabbit, which is the offspring of the European 
rabbits placed on that island in 1419,-will not breed now 
with the posterity of its European ancestor. Further, it 
does not follow, because mules are unreproductive, that all 
other hybrids have been, and will be. Thus, the Lepus 
Darwinii, originally resulting from the crossing of the 
Rabbit and Hare, now reproduces its kind, the animal 
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