236 MORPHOLOGY. [Chap. XIV. 



tacean, 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, stamens, and 

 pistils, in each flower, though fitted for such distinct 

 purposes, be all constructed on the same pattern ? 



On the theory of natural selection, we can, to a 

 certain extent, answer these questions. We need not 

 here consider how the bodies of some animals first 

 became divided into a series of segments, or how they 

 became divided into right and left sides, with corre- 

 sponding organs, for such questions are almost beyond 

 investigation. It is, however, probable that some serial 

 structures are the result of cells multiplying by division, 

 entailing the multiplication of the parts developed from 

 such cells. It must suffice for our purpose to bear in 

 mind that an indefinite repetition of the same part or 

 organ is the common characteristic, as Owen has 

 remarked, of all low or little specialised forms ; there- 

 fore the unknown progenitor of the Vertebrata probably 

 possessed many vertebne ; the unknown progenitor of 

 the Articulata, many segments ; and the unknown 

 progenitor of flowering plants, many leaves arranged in 

 one or more spires. We have also formerly seen that 

 parts many times repeated are eminently liable to vary, 

 not only in number, but in form. Consequently such 

 parts, being already present in considerable numbers, 

 and being highly variable, would naturally afford the 

 materials for adaptation to the most different purposes ; 

 yet they would generally retain, through the furce of 

 inheritance, plain traces of their original or fundamental 

 resemblance. They would retain this resemblance all 

 the more, as the variations, which afforded the basis for 



