SOME CONSEQUENCES OF EVOLUTIONARY RELATIONSHIP 357 



show homologous resemblance. It is common to find homologous struc- 

 tures repeated in the body of a single organism. Examples are the spirally 

 or cyclically repeated leaves and flower parts of angiosperms and the 

 serially or radially repeated parts of vertebrates, arthropods, annelid 

 worms, and echinoderms. Such repeated parts may be duplicates of one 



Fig. 24.2. "The Bear Hunt," showing skeletal homologies in mammals. Prepared by 

 Charles H. Ward for the Chicago Fair of 1893. (Courtesy Ward's Natural Science Establish- 

 ment, Inc.) 



another or may differ strongly in form and function. Leaves, petals, and 

 stamens are homologous in spite of their differences. The paired legs of 

 centipedes are all much alike; but in such an arthropod as the lobster the 

 homologous segmental appendages are modified into feelers, jaws, pincers, 

 legs, copulatory organs, and swimming paddles. 



Homology may also be seen in the corresponding structures of indi- 

 viduals belonging to the same species or to related species. In individuals 

 of the same species the homology is complete, for the corresponding parts 



