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CHAPTER XVIII. OTHER THEORIES OF SPECIES-FORMING ... 263 



Theories Auxiliary to Natural Selection 263 



Weismann's Theory of Panmixia 263 



Weismann's Theory of Germinal Selection 265 



Roux's Theory of Intraselection or the Battle of the Parts . . 268 



Coincident Selection or Organic Selection 268 



Isolation Theories 269 



Theories Alternative to Natural Selection 273 



CHAPTER XIX. A NEW COMPOSITE CAUSO-MECHANICAL THEORY 

 OF EVOLUTION (THE TETRAKINETIC THEORY). Henry Fair field 



Osborn 275 



The Energy Concept of Life 275 



The Four Complexes of Energy 280 



PART IV. GENETICS 



CHAPTER XX. THE SCOPE AND METHODS OF GENETICS .... 287 



Definitions 287 



The Scope and Methods of Genetics 287 



The Importance of the Cell Theory in Genetics 289 



CHAPTER XXI. THE BEARERS OF THE HERITAGE (an Account of the 



Cellular Basis of Heredity). Michael F. Guyer 290 



CHAPTER XXII. VARIATION. Ernest Brown Babcock and Roy 



Elwood Clausen 307 



CHAPTER XXIII. ARE ACQUIRED CHARACTERS (MODIFICATIONS) 



HEREDITARY? 323 



Misunderstandings as to the Question at Issue. /. Arthur Thom- 

 son 323 



The Inheritance or Non-Inheritance of Acquired Characters. 



Edwin Grant Conklin 330 



The Other Side to the Question 33 6 



A Possible Mechanism for the Transmission of Acquired Characters. 



Michael F. Guyer 338 



CHAPTER XXIV. THE MUTATION THEORY 346 



New Species (Mutants) of Oenolhera. Hugo De Vries .... 348 



Summary of De Vries's Mutation Theory. Thomas Hunt Morgan . 355 



Criticisms 359 



Causes of Mutations 360 



CHAPTER XXV. BIOMETRY (THE STATISTICAL STUDY OF VARIATION 



AND HEREDITY). H.H.N 365 



The Statistical Study of Variation 365 



Bimodal and Multimodal Curves 368 



The Coefficient of Correlation 369 



Statistical Study of Inheritance. Edwin Grant Conklin . . . 370 



