Chap. XIII. MORPHOLOGY. 437 



become extremely different, are at an early stage of 

 growth exactly alike. 



How inexplicable are these facts on the ordinary 

 view of creation ! Why should the brain be enclosed 

 in a box composed of such numerous and such extra- 

 ordinarily shaped pieces of bone? As Owen has re- 

 marked, the benefit derived from the yielding of the 

 separate pieces in the act of parturition of mammals, will 

 by no means explain the same construction in the skulls 

 of birds. Why should similar bones have been created 

 in the formation of the wing and leg of a bat, used as 

 they are for such totally different purposes? Why 

 should one crustacean, which has an extremely complex 

 mouth formed of many parts, consequently always have 

 fewer legs ; or conversely, those with many legs have 

 simpler mouths? Why should the sepals, petals, sta- 

 mens, and pistils in any individual flower, though fitted 

 for such widely different purposes, be all constructed 

 on the same pattern ? 



On the theory of natural selection, we can satisfactorily 

 answer these questions. In the vertebrata, we see a series 

 of internal vertebrae bearing certain processes and appen- 

 dages ; in the articulata, we see the body divided into a 

 series of segments, bearing external appendages ; and in 

 flowering plants, we see a series of successive spiral 

 whorls of leaves. An indefinite repetition of the same 

 part or organ is the common characteristic (as Owen 

 has observed) of all low or little-modified forms ; there- 

 fore we may readily believe that the unknown progenitor 

 of the vertebrata possessed many vertebra? ; the unknown 

 progenitor of the articulata, many segments ; and the 

 unknown progenitor of flowering plants, many spiral 

 whorls of leaves. We have formerly seen that parts many 

 times repeated are eminently liable to vary in number 

 and structure; consequently it is quite probable that 



