138 HEREDITY [ap. 



unimaginable. The Theory of Pangenesis never gained 

 any very wide acceptance, but is of great importance 

 owing to its stimulating effect on later work and 

 thought. To a gi-eat extent it led to the formulation 

 of other theories of heredity \ any account of which is 

 prevented by limitation of space. It can only be 

 mentioned that the chief hypotheses which followed 

 Darwin's laid successively more and more emphasis 

 upon the idea that the germ-cells are not made up of 

 samples taken from the body, but have a certain 

 independence. So gi-ew up the conception of 'germinal 

 continuity,' that is, the idea that the germ-cell of one 

 generation gives rise not only to the body of the next, 

 but also directly to its germ-ceils, so that the body 

 does not produce germ-cells, but only contains them. 

 We must now turn to the theory in which this idea finds 

 its most celebrated expression, AVeismann's Theory 

 of the Germ-2)lasm (1885) [40, 8]. 



It is impossible in a short space to give an 

 adequate account of Weismann's great theory, which 

 he has worked out in fuller minuteness of detail than 

 has been done with any other theory of heredity, and 

 by which he has done more to stimulate discussion 

 and research than perhaps any biologist since Darwin. 



^ For a summary of the more important theories of heredity, 

 especially those of Herbert Spencer (1863, i.e. before Darwin's theory 

 of Pangenesis), Galton (1875) and de Viied (1889), see Thomson's 

 Heredity [33]. See also [8]. 



