II GRADUATED EVOLUTION 31 



system to which we may with Nageli give the general name 

 kinships {Sippen). It would therefore be more appropriate 

 in general to speak of the origin of kinships than of the origin 

 of species. 



We have then before us a graduated evolution, and the 

 essential cause of the separation of species is seen to be the 

 persistence of a number of individuals at a definite lower 

 grade of this evolution, while the rest advance farther in 

 modification. This mode of origin of varieties or species, as 

 the case may be, I have named Genepistasis {yevo^ race, 

 iiTicrraai'; stand still). 



With the facts and laws set forth by me in the previous 

 pages as the foundations of my theory of the organic growth 

 of the species, compare Wurtenberger : A Nevj Contribution to 

 the Zoological Proof of the Dariuinian Theory, Ausland, 1873, 

 JSTos. 1 and 2, and Studies on the History of the Descent of the 

 Ammonites. A Zoological Proof of the Dartuinian Theory. 

 Leipzig, 1880. 



Wurtenbers^er finds that in Ammonites all structural 

 changes show themselves first on the last (the outer) whorl 

 of the shell — as in living animals, e.g. in my lizards ^ at the 

 tail — and that then such a change in the following genera- 

 tions is pushed farther and farther towards the beginning of 

 the spiral — as e.g. in my lizards towards the head — until it 

 prevails in the greater number of the whorls. 



Then still newer characters may arise again on the most 

 external whorl — just as in lizards at the tail — and drive back 

 the former, and so on. The Ammonites also only at an 

 advanced age, only when they have as exactly as possible 

 gone through the course of development inherited from their 

 parents, acquire the power to vary in a new direction ; but 

 this power can be inherited in such a way that in following 



^ See my memoirs, Ueher das Variiren der Manereidechse, and on the markings 

 of mammals and birds of prey. 



