HEREDITY 225 



is reserved to form the reproductive material of the 

 mature offspring." Unfortunately for the theory as 

 put forward by Jaeger, embryological investigations 

 failed to show that this supposed continuity of the 

 germinal cells actually existed save in a very few instances. 

 Weismann's adaptation of Jaeger's theory aimed at 

 getting over this crucial difficulty in the following way. 

 He held that a certain part of the fertilised ovum is, so 

 to speak, put on one side from the very commencement 

 of the developmental process to serve as a starting-point 

 for the germ cells of the new organism, and to this hypo- 

 thetical substance he gave the name of "germplasm." 

 The germplasm is a part of the nucleus of extremely 

 complex structure which has the power of growing and 

 yet of retaining its primitive characters unaltered. 

 Part of it, however, is changed into the nuclei of the 

 ordinary somatic cells while retaining enough of its 

 original efficiency to start a new organism asexually if 

 need be. As Galton puts it, according to the Weismannian 

 hypothesis, " the main line may be rudely likened to the 

 chain of a necklace and the personalities to pendants 

 attached to the links." 



One important consequence of Weismann's work 

 was to call in question the validity of the view that any 

 modification of the individual induced by external 

 conditions during its lifetime, in other words, an " acquired 

 character," would be transmitted to the offspring. If, 

 as Weismann thought, germplasm and somatoplasm were 

 initially distinct, and if the germplasm was alone concerned 

 in the transmission, it was obvious that modifications 

 of the somatoplasm could not be transmitted, that any 

 structural change in a part of the body induced by use 

 or disuse, or by environmental or nutritive influences 

 generally, never affects the germplasm in such a way 

 as to cause the offspring to exhibit the modification that 

 the parent had acquired, or even to show a tendency 

 in that direction. 



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