NATURAL SELECTION 79 



existing species have, in all likelihood, been formed 

 or accumulated during many changes of environment, 

 caused by changes in the surface of the globe, com- 

 pelling the various species to separate and disperse, 

 and so come under diverse external conditions. The 

 multitude of rudimentary or atrophied organs, that 

 seem to be more numerous the higher the type, point 

 to far remote ancestral genera, that differed greatly 

 in form, structure, and function from the existing 

 forms ; while the many cases of what is called 

 reversion point to the characteristics of more recent 

 but still extinct genera. To this category belongs the 

 frequent recurrence of stripes in individuals of species 

 that do not generally show them, as in the young of 

 equine animals, telling of their descent from pro- 

 genitors that were distinguished characteristically by 

 stripes. Though occurring in individuals of existing 

 species, they cannot be regarded as individual differences, 

 but must be considered as generic characteristics, that 

 have come to the surface from a principle of inheritance, 

 that, under the changed conditions of existence, is 

 slowly dying out, but is still sufficiently active to 

 assert its power in a faint sporadic fashion. 



On the other hand, we have naturally formed 

 varieties of species, that have not yet attained to rank 

 as species, which have been formed under the action 

 of new external conditions, giving them a certain 

 differentiation from the parent, and also from one 

 another. The characteristic of varietal, as apart from 

 specific forms, is that the reproductive organs have 



