394 DARWINISM TO-DAY. 



formation of species should be the object of direct observation. It 

 is generally understood in the natural sciences either that direct 

 observation should form the foundation of our conclusions or 

 mathematical laws, which are derived from direct observations. This 

 rule was evidently considered superfluous by those writing on the 

 hypothesis of evolution. Their scientific conscience was quieted by 

 the assumption that processes like that of evolution could not be 

 directly observed, as they occurred too slowly, and that for this 

 reason indirect observations must suffice. I believe that this lack 

 of direct observation explains the polemical character of this liter- 

 ature, for wherever we can base our conclusions upon direct obser- 

 vations polemics become superfluous. It was, therefore, a decided 

 progress when de Vries was able to show that the hereditary 

 changes of forms, so-called 'mutations,' can be directly observed, at 

 least in certain groups of organisms, and secondly, that these 

 changes take place in harmony with the idea that for definite 

 hereditary characteristics definite determinants, possibly in the form 

 of chemical compounds, must be present in the sexual cells. It seems 

 to me that the work of Mendel and de Vries and their successors 

 marks the beginning of a real theory of heredity and evolution. If 

 it is at all possible to produce new species artificially, I think that 

 the discoveries of Mendel and de Vries must be the starting point." 



8 Schmankewitsch, A., Zeitschr. f. iviss. Zool., Vol. XXV, p. 103, 

 1875 ; also Zeitschr. f. iviss. Zool., Vol. XXIX, p. 429, 1877. 



9 Adelung, Zool-Centralbl, Vol. VI, p. 757, 1899. (A review of 

 Anikin's paper, which is in Russian.) 



10 Kellogg, V. L., "A New Artemia, and Its Life-Conditions," 

 Science, N. S., Vol. XXIV, 594-596, 1906. 



11 Klebs, G., "Willkiirliche Entwickelungsanderungen bei Pflan- 

 zen," 1903. 



12 Tower, W. L., "Evolution in Chrysomelid Beetles of the Genus 

 Leptinotarsa," Pub. No. 48, Carnegie Institution of Washington. 



"The phenomenon of variation primarily owes its existence to the 

 fact that community of descent and heredity tends to produce the 

 exact counterpart of the parent organisms ; the process of develop- 

 ment, however, is not carried out under absolutely constant or uni- 

 form conditions, but in a world wherein there exist changing environ- 

 mental states in endless proximity. This results in the turning 

 aside in the line of development from the parental standard, per- 

 haps ever so little or only in one character ; but in this we have 

 deviation or variation" (p. 298). 



"In the explanation of origin of variation in organisms the only 

 assumption we need make is that the original unit of organic matter 

 was possessed of the attributes which characterise organic matter 



