692 Mutations 



mutable condition, but of course thousands of 

 mutations must have been required to produce 

 the immediate ancestors of the evening-prim- 

 roses from the original stock. 



If we now take the species into considera- 

 tion that are not mutable at present, we may 

 ask how we are to combine them with each of 

 the two theories proposed. If mutability is 

 permanent, it is manifest that the whole pedi- 

 gree of the animal and vegetable kingdom is to 

 be considered as built up of main mutable lines, 

 and that the thousands of constant species can 

 only be taken to represent lateral branches of 

 the genealogic tree. 



These lateral branches would have lost the 

 capacity of mutating, possessed by all their an- 

 cestors. And as the principle of the hypothesis 

 under discussion does not allow a resumption of 

 this habit, they would be doomed to eternal con- 

 stancy until they finally die out. t Loss of muta- 

 bility, under this conception, means loss of the 

 capacity for all further development. Only 

 those lines of the main pedigree which have 

 retained this capacity would have a future ; all 

 others would die out without any chance of pro- 

 gression. 



If, on the other hand, mutability is not perma- 

 nent, but a periodic condition, all lines of the 

 genealogic tree must be assumed to show alter- 



