2 26 Heredity and Eugenics 



investigation. The dogma of the irreversibility of evolution 

 processes, which has grown out of phylogenetic and onto- 

 genetic study, is incompatible with a physico-chemical in- 

 terpretation of nature, and has no basis at present in critical 

 experimental investigation. 



These germinal modifications of color characters indicate 

 an approach to an understanding of germinal variations in 

 certain attributes; that is, it is understood what might 

 happen, but in no case is it known what did happen, nor 

 how. These variations in color concern superficial attributes 

 in the economy of the organism; and the mere production 

 of a color-producing substance is to a greater or less extent 

 only an incident in the life of the organism. Colors are 

 produced pathologically or otherwise in these organisms, 

 by wounding, by disease, etc., at will, showing that there is 

 throughout the organism the capacity for the production 

 of color compound which lies at the basis of the normal 

 coloration. The greater problem lies not in the production 

 of color changes, but in the processes which are productive 

 of the localization of pigments into a color pattern, and it is 

 this attribute of pattern which differentiates organisms most 

 certainly from inorganic substances. What is it that is 

 productive of pattern, and in which way may the color be 

 modified ? 



Experimental modification of pattern. — The pattern is an 

 attribute by no means so easy to modify as is color, but it 

 has been found that the pattern is less modifiable by incident 

 forces than other parts of the organism. Of those instances 

 in which the pattern has been modified, as in alhida, tortuosa, 

 minuta, and dejecta punctata (Fig. 73C), all proved to be 

 germinal variations and to breed true, but the difficulty in 

 breeding many of them and their inability to exist under 



