472 THE EVOLUTION OF LIFE. 



numerous lateral appendages wliicli, in the lower crustaceans, 

 most of them serve as legs, and have like shapes, are, in the 

 higher crustaceans, some of them represented by enormously- 

 developed claws, and others by variously-modified foot-jaws. 

 " It is familiar to almost every one," he continues, " that in 

 a flower the relative position of the sepals, petals, stamens, 

 and pistils, as well as their intimate structure, are intelli- 

 gible on the view that they consist of metamorphosed 

 leaves arranged in a spire. In monstrous plants we often 

 get direct evidence of the possibility of one organ being 

 transformed into another; and we can actually see in 

 embryonic crustaceans and in many other animals, and in 

 flowers, that organs, which when mature become extremely 

 different, are at an early stage of growth exactly alike." 

 . . . " Why should one crustacean, which has an ex- 

 tremely 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 any individual flower, though fitted 

 for such widely-different purposes, be all constructed on the 

 same pattern ? " 



To these and countless similar questions, the theory of 

 evolution furnishes the only rational answer. In the course 

 of. that change from homogeneity to heterogeneity of struc- 

 ture displayed in evolution under every form, it will neces- 

 sarily happen that from organisms made up of numerous like 

 parts, there will arise organisms made up of parts more and 

 more unlike: which unlike parts will nevertheless continue 

 to bear traces of their primitive likeness. 



§ 135. One more striking morphological fact, near akin 

 to some of the facts dwelt on in the last ' chapter, must be 

 here set down — the frequent occurrence, in adult animals 

 and plants, of rudimentary and useless organs, which are 

 homologous with organs that are developed and useful in 

 allied animals and plants. In the last chapter we saw that 



