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EVOLUTION AND CONSERVATION 



Part VI 



ARBOREAL 

 Climbing 



TERRESTRIAL 

 Short, pentadactyl 

 limbs 



CURSORIAL 

 Running 



AQUATIC 



> Swimming ^«^<.«r.... 



^ FOSSDRIAL 



Burrowing 



Fig. 38.5. The structure of the Hmbs of mammals that live in different environ- 

 ments. At the center is a primitive 5-toed terrestrial mammal. The other figures 

 show other mammals related to the central one but adjusted to particular environ- 

 ments and ways of living in them. This is called adaptive radiation. (Courtesy, 

 Moody: Introduction to Evolution. New York, Harper & Bros., 1953.) 



Heredity — A Force in Evolution 



Heredity produces both unity and diversity. It maintains old fundamental 

 structures and activities and it establishes the new features known as mutations 

 that partly account for the entrancing variety of nature. 



Inheritance of Ancestral Pattern in Embryos. Except in some special types 

 of reproduction, every multicellular animal begins life as one cell, a fertilized 

 egg which divides into two cells, and goes on according to the course of its 

 ancestors. The embryos of various invertebrates show striking similarities, 

 maintained by inheritance and expressive of kinship. Those of various groups 

 of animals are figured and described in Part 5, Evolution of Animals. In- 

 heritance of ancestral pattern in embryos includes only the oldest and most 

 fundamental structures. In the vertebrates, these are the notochord, the ver- 



