170 THE THEORY OF EVOLUTION 



exceptions, however, are certainly known (Quince and 

 Apple). Hence, by crossing, it is only a question of 

 new combinations of specific characters which are of 

 quite subordinate nature, such as colour and size. In 

 order that the new forms should remain constant 

 strict in-breeding is necessary, which, in most cases, 

 can only be artificially ensured. Consider only Mendel's 

 experiments. That by crossing the ' analytical formula 

 of an organism ' may be ever discovered is a dream. 



Some palseontological series and many observations 

 of the present organisms permit of recognition that 

 even quite gradual transitions lead from one to another 

 species, especially the evidence of convergence and 

 ' specialization/ 1 



All these observations tell us obviously only how, 

 by suddenly appearing mutations, by crossing and by 

 gradual change in determined directions (caused indeed 

 by gradually changing environment), new forms appear 

 within the limits of definite organic types. 



(2) Suggestions derived from animal and plant geo- 

 graphy concerning the origin of transformations." 



It is not all deviations which appear in the progeny 

 of the same animal or plant parents which can be 

 imputed to the influence of changed environment. 



1 Deperet-Wegner : Die Umbildung der Tierwelt, p. 138. 



2 See J. P. Lotsy, Vorlesungen iiber Descendenztheorien, II, p. 483 ; 

 R. Heffe, Abstammungslehre und Darwinismus, p. 44 ; A. Wei smarm : 

 Vortrdge iiber Descendenztheorie, II, p. 235 ; Einfluss der Isolierung auf 

 die Arfbildung ; L. Plate, Selectionsprinzip und Probleme der Arfbildung, 

 Leipzig, 1908, p. 396. 



