50 LABORATORY DIRECTIONS IN 



ever, a fairly complete series of fossils demonstrates the transition from 

 the many-toed ancestor to the one-toed modern horse,. This series of 

 fossils should be examined at the present stage of the work but a careful 

 study of them will be deferred until the exercise in paleontology. 



D. SUMMARY 



What is homology? What evidence of homology in the foregoing 

 study? Must adult structures be different from one another in order 

 to exhibit homology? Must embryonic structures be alike in order to 

 exhibit homology? Are the wings of two robins homologous with each 

 other? In what ways do the vertebrate limbs differ among themselves? 

 What is the commonest kind of modification from the supposed ancestral 

 type? Which of the limbs studied is the most modified from the ancen- 

 tral type? Which least modified? On the basis of the structure of the 

 limbs, does man stand high or low in the animal series? Of what use is 

 homology in other branches of zoology? 



The above questions are a guide only to the contents of the summary 

 not to the order of presentation. 



References 



ROMANES, GEORGE J., "Darwin and After Darwin," Vol. 1, Chapters III and IV. 

 SCOTT, WILLIAM B., "The Theory of Evolution," pp. 42-73. 



