ORIGIN OF ADAPTATIONS AND OF SPECIES 243 



tion. This progressive acclimatization of successive genera- 

 tions of an organism to heat is clearly due in large measure to 

 heredity. So also in the case of the entomostracan Artemia, 

 whose specific form Schmankewitsch succeeded in changing, 

 by increasing the salinity of the water in which the animal 

 lived. Here, again, the adaptation was brought about with- 

 out the aid of selection. 



Poulton's already-mentioned experiments on larvae and 

 pupae show that these may become protectively colored as the 

 direct effect of the surrounding light on the organism. Here, 

 of course, the possible influence of natural selection can scarcely 

 be excluded, though the fact remains that the color resem- 

 blances are initiated directly by the stimulus of light upon 

 protoplasm. 



Protoplasm itself is to a certain extent adaptive, in that it 

 may become acclimatized to untoward conditions of heat, light 

 and other stimuli. From this point of view, Henslow's theory 

 of self-adaptation in plants deserves more consideration than 

 it has received, though Henslow did not adopt the theory of 

 natural selection. 



Blastogenic Variations. According to Weismann, only 

 congenital variations are inheritable, i. e., only those that result 

 from modifications of the germ plasm. He holds that while 

 all variations are due ultimately to external influences, the 

 processes of reproduction (conjugation in unicellular, and 

 sexual reproduction in multicellular organisms) furnish fresh 

 combinations of individual variations for the operation of nat- 

 ural selection, and that this is the chief purpose of amphimixis, 

 or " the mingling of two individuals or of their germs." 



Inheritance of Acquired Characters. Weismann and his 

 followers, in opposition to the Neo-Lamarckians, hold that 

 somatogenic, or acquired, characters are not transmissible; 

 that every permanent (hereditary) variation proceeds from 

 the germ. 



The subject of the inheritance of acquired characters has 

 aroused no end of discussion, much of which has been fruit- 



