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THE AMERICAN NATURALIST [Vol. XLV 



pear from which they had all but disappeared is a regres- 

 sion or return to the condition of the greater majority of 

 the group, a condition which must have been shared by 

 its ancestors at no remote stage in its progressive 

 development. 



None of the attempts hitherto made to perfect a theo- 

 retical conception which would be useful in interpreting 

 the mechanism of environic responses have had anything 

 more than the most limited usefulness. The stimuli of 

 climatic and many other agencies do not imply the intro- 

 duction of any strange or new substances into the bodies 

 of the organs affected. These agencies might change the 

 dissociations in such a manner as to modify the relative 

 number of free ions and thus alter the molecular complex 

 of the living matter in a very important manner. The 

 intricate play of enzymatic action might also be altered, 

 and any modification of the relative reaction velocities of 

 the more important processes might result in material 

 and permanent change, especially in those cases in which 

 external agencies interfere directly with the action of the 

 germ-plasm. 



The introduction of solutions into ovaries or the ex- 

 posure of reproductive elements to unusual irradiation 

 may raise the additional liability of disturbed polarity 

 and of modified surface tensions in the cells. It is conceiv- 

 able that the rearrangement or disturbance of the local- 

 izations of substances, especially the mineral salts, might 

 seriously modify the capacities of the bearers of heredity. 

 These direct and material possibilities offer an adequate 

 basis for the organization of experimental research upon 

 the main subject, as well as the means of interpretation 

 of results without recourse to schemes of particulate 

 inheritance or theories as to the constitution of germ- 

 plasm to which may be ascribed usefulness in the discus- 

 sion of other problems in evolution. 



The theoretical consideration of the subject which seeks 

 to assign all cases of inheritance of environic effects to 

 the direct action of the existing agency upon the germ- 

 plasm in itself is one to be regarded with some wariness, 

 as it may lead us into empiric assumptions which may 



