78 HEREDITY AND VARIATION 



been taken advantage of in breeding sheep with long fleece, 

 Japanese cocks with tails ten feet long, "wonder horses" with 

 manes reaching the ground, and so on. 



The recognition of minus and plus variations is simple and 

 obvious, but it is not sufficient. For the offspring is sometimes 

 so different from the parent that we cannot describe its pecu- 

 liarity as an incompleteness in the expression of the normal 

 inheritance, or as an exaggeration of parental or ancestral traits. 

 It is sometimes a new pattern, a fresh departure, with what one 

 might call organic originality. It is more than a discontinuous 

 variation, for when the offspring of a horned race has no horns, 

 or when the offspring is a giant, there is " discontinuity," — an 

 abrupt difference between parents and offspring. But what 

 we are referring to here are those cases where the offspring 

 seems to have passed suddenly into a new position of organic 

 equilibrium, where it has not only individuality, but a dis- 

 tinctively novel individuality. It is convenient to call these 

 variations by the special name mutations. They are novelties 

 which arise brusquely. 



§ 5. Fluctuating Variations 



When we examine a number of individuals of the same species 

 we usually find that they differ from one another in detail. 

 Some of the observed differences may be modificational or due 

 to differences of nurture, but it is often possible to abstract 

 these from differences due to hereditary nature. Thus, when 

 we coUect a large number of specimens of the same age 

 from the same place at the same time, we often find that 

 no two are exactly alike. They have peculiarities of germinal 

 origin — or, in other words, they show individual or fluctuating 

 variations. Measurements in regard to any one character 

 can be readily plotted out, and the result gives the curve of 

 frequency. 



