VARIATION IN ANIMALS AND 



PLANTS. 



PART I. 

 THE FACTS OF VAEIAT10N. 



CHAPTER I. 



THE MEASUREMENT OF VAKIATION. 



Variation studied from the mathematical standpoint Variation of 

 birds diagrammatically represented Distribution of crab measure- 

 mentsNormal 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 Mean Error, and Error, of Mean Square Examples of 

 asymmetrical series Representation of these by a generalised 

 mathematical expression. 



IF a number of individuals of any species be com- 

 pared, it will be found that they all show differences 

 from each other either in size, shape, colour, relation 

 of parts, or other characteristics; in fact, no two of 

 them are exactly alike. Even if offspring be compared 

 with their own parents, similar, though on the whole 

 not such marked, differences will present themselves. 

 These differences constitute what is known as Varia- 

 tion, and it is into the facts of this variation, and its im- 



