VARIATION 423 



consequence of a change in nutrition, some of these deter- 

 minants F in different individuals constantly vary in such 

 a manner that if they were in the majority in the germ- 

 plasm they would give rise to a white spot instead of a 

 black one. It will sometimes happen that they are in the 

 majority ; for, in consequence of the process of amphimixis, 

 the modified determinants F may become accumulated in the 

 course of generations, so as to exceed fifty in one or more 

 individuals. The black spot will then turn white, and among 

 thousands of individuals belonging to this species some will 

 exhibit this variation. 



The subsequent course of the phyletic development of this 

 white spot depends upon its physiological value to the species. 

 Even if it is only of slight importance, it will gradually come to 

 be possessed by an increasing number of individuals, and will 

 ultimately be traasm.itted to all of them : i.e., it will become a 

 specific character. This extension could hardly occur without 

 amphimixis ; for by its means any minority of determinants 

 F^ wherever produced, may accumulate so as to constitute a 

 majority ; and otherwise they could not have been effective, 

 since a minority could never have produced a white spot. 



This example was selected because it is based on facts. A 

 variety of Lycana agestis actually exists which possesses a 

 milky-white spot on each of the four wings in the place of the 

 black one ; it is known as the variety artaxerxes., and occurs 

 in the north of England. It is immaterial whether se.xual selec- 

 tion or a protective resemblance has caused the dominance of 

 this modification. 



Many variations of one species or another are merely due to 

 the modification of a few or a large number of determinants ; 

 changes in the colour of individual parts or of the whole body 

 may occur without an accompanying increase in the total number 

 of determinants of the germ-plasm, but, on tlie other hand, as 

 was shown above, many modifications do result from an increase 

 in their total miniber. We have already seen that the doubling of 

 a determinant of the germ-plasm may be referred to the influences 

 of nutrition, and no difficulties therefore arise in the application 

 of the principle just propounded to the multiplication of the 

 determinants. The important modifications in species, includ- 

 ing all enlargement of parts and higher differentiation of organs, 

 must be connected with this increase : and the accumulation 



