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CHAPTER XIV. 



MODIFICATION AND VAEIATION. 



UP to a time still comparatively recent, the transmission 

 to offspring, in greater or less degree, of those modifica- 

 tions of habit or structure which the parents had acquired 

 in the course of their individual lifetime, was generally 

 accepted. Lamarck is regarded as the intellectual father 

 of these the transmissionists. In his "Histoire Natu- 

 relle" he said, "the development of organs and their 

 power of action are continually determined by the use of 

 these organs." This is known as his third law. In the 

 fourth he insisted on the hereditary nature of the effects 

 of use ; "all that has been acquired, begun, or changed," 

 he said, " in the structure of individuals during the course 

 of their life, is preserved in reproduction and transmitted 

 to the new individuals which spring from those which 

 have experienced the changes." 



Darwin accepted such transmission as subordinate to 

 natural selection, and attempted to account for it by his 

 theory of pangenesis. According to that hypothesis all 

 the component cells of an organism throw off minute 

 gemmules, and these and their like, collecting in the 

 reproductive cells, are the parental germs from which all 

 the cells of the offspring of that organism are developed. 

 This theory, here given in briefest outline, came in for its 

 full share of criticism. The problems of heredity were 

 recognized as being of supreme biological importance and 



