414 EVIDENCES OF EVOLUTION 



complete name of the lion is Felis leo, of the tiger, Felis 

 tigris, etc. — names that are fixed and known by the 

 entire scientific world. Every species, genus, family, and 

 higher division of both the plant and animal kingdom 

 has its own particular scientific name. 



Comparative Anatomy. — As indicated in a former 

 paragraph, evidence from superficial resemblances be- 

 tween the various species of animals and plants is not 

 a safe guide in classification. On such a basis the whale 

 and fish would be close relatives. Actually, they are no 

 more closely related than man and a shark. The resem- 

 blance is merely one of analogy, a similarity of form. 

 Wings are analogous organs in birds and insects. In both 

 groups there is a likeness of function, but structurally 

 they are very different and only distantly related. 



On the other hand, the wing of a bat and the arm of 

 man present no analogies of either form or function. 

 They are, however, fundamentally alike in structure 

 (Fig. 121). Bone for bone, muscle for muscle, nerve 

 for nerve, they are almost identical, the difference 

 being merely those of proportion. Extending the com- 

 parison, it is found that the wings of birds, the paddles 

 of whales, the digging arms of moles, the legs of 

 horses, zebras, etc., present wide differences of form 

 anrl function, and yet are structurally nearly alike. 

 Other parts of the body illustrate the same fact. This 

 deep-seated identity of structure is termed homology, 

 and is interpreted as a sign of blood relationship. Just as 

 the modern one-fingered horse has been derived from a 

 five-fingered ancestor, so, it is believed, all of the back- 

 boned animals or vertebrates, with their various types of 

 limbs, are the descendants of a remote ancestral species. 



Rudimentary or Vestigial Organs. — In the search 

 for homologies among the various species of animals and 

 plants, organs have come to light, especially among the 

 higher species, which are of little or no use. In the 

 modern horse, for example, two small splint bones occur 



