THE BRIDGE OF LIFE 



491 



muscles of his arms became highly developed, then the pangenes formed 

 in these muscles would migrate and become a part of his sperms. If 

 this blacksmith then had a child, this child would have strong arms 

 because of these pangenes. 



It remained for a German, August Weismann, to disprove these 

 various theories on the inheritance of acquired characteristics. He 

 cut the tails off a group of new-born mice and when they reproduced, 

 the tails were cut from the offspring and so on for twenty generations. 

 When the twenty-first generation appeared the tails were allowed to 

 grow and these had tails just as long as other mice that did not have 



GERM -PLASM 

 THEORY 



# - - Germ plasm 

 (7*. - - Somatoplasm, 



Other parent 



Other parent 



PANGENESIS 

 THEORY 



Other parent 'I Other parent 



From Genetics, Winchester, Houghton Mifflin 

 Fig. 31.2. Weismann's germ-plasm theory contrasted with Darwin's pangenesis theory. 



a history of tail-clipping in their ancestry. From this and other studies 

 he concluded that the reproductive cells were carried by animals, but were 

 not influenced by the activities of these carriers. He spoke of the cells 

 directly involved in reproduction as the germ plasm and the rest of the 

 body as the somatoplasm. He maintained that the germ plasm formed 

 a continuous stream from generation to generation producing the 

 somatoplasm, but not being altered by it. Fig. 31.2 shows the distinc- 

 tions between the pangenesis theory of Darwin and the germ-plasm 

 theory of Weismann. The accumulating evidence from many sources 

 has led geneticists to accept Weismann's viewpoint that the germ plasm 

 is not influenced by the somatoplasm — in other words, that there is no 

 inheritance of acquired characteristics. A person can transmit to his 

 offspring only those genes which he received from his parents. We do 



