CONTENTS. 



PART I. 

 THE FACTS OF VARIATION. 



CHAPTER I. 

 THE MEASUREMENT OF VARIATION. 



PAGE 



Variation studied from the mathematical standpoint Vari- 

 ation of birds diagrammatically represented Distribution 

 of crab measurements Normal curve of error Its relation ^ 

 to binomial curve Variations in animals and plants 

 subject to Law of Frequency of Error Measurement of 

 variation in terms of Probable Error, Arithmetic Meant 

 Error, and Error of Mean Square Examples of Asym- / 

 matrical series Representation of these by a generalised 

 mathematical expression, 1 



CHAPTER H. 

 DIMORPHISM AND DISCONTINUOUS VARIATION. 



Dimorphism in the earwig and in the crab How to dis- 

 tinguish between species and varieties, as instanced by 

 dimorphism in certain fishes, and in a marsh plant Poly- 

 morphism in plants Series of Fibonacci Discontinuous 

 variation in animals as regards vertebrae, ribs, mammae, 

 teeth, digits, and other characters Homceosis De Vries' 

 Theory of Mutation Dimorphism may be due to internal 

 causes, or the result of divergent evolution Physiological 

 Selection Infertility between varieties, . , .37 



