xix HEREDITY 367 



they arose. At dates so widely separate as are suggested 

 by the names of Democritus and Hippocrates, Paracelsus 

 and Buffon, the same idea was expressed that the germs 

 consist of samples from the various parts of the body. 

 But the theories of these authors were vague and in some 

 respects entirely erroneous suggestions. The best- 

 known form of this type of theory is Darwin's ' pro- 

 visional hypothesis of pangenesis ' (1868), according to 

 which (a) every cell of the body, not too highly differ- 

 entiated, throws off characteristic gemmules, which 



(b) multiply by fission, retaining their peculiarities, and 



(c) become specially concentrated in the reproductive 

 elements, where (d) in development they grow into cells 

 like those from which they were originally given off. 

 This theory was satisfactory in giving a reasonable 

 explanation of many of the facts of heredity ; it was 

 unsatisfactory because it involved many unverified hypo- 

 theses. 



3. The Idea of the Continuity of Generations. In 1876 

 Jaeger expressed his views explicitly as follows : 



' Through a long series of generations the germinal protoplasm 

 retains its specific properties, dividing in development into a portion 

 which is reserved to form the reproductive material of the mature 

 offspring." 



This reservation, by which some of the germinal proto- 

 plasm is kept apart, during development and growth, 

 from corporeal or external influences, and retains its 

 specific or germinal characters intact and continuous with 

 those of the parent ovum, Jaeger regarded as the funda- 

 mental fact of heredity. 



Brooks (1876, 1877/1883) was not less clear: 



' The ovum gives rise to the divergent cells of the organism, but 

 also to cells like itself. The ovarian ova of the offspring are these 

 latter cells or their direct unmodified descendants. The ovarian 

 ova of the offspring thus share by direct inheritance all the proper- 

 ties of the fertilised ova." 



But before and independently of either Jaeger or Brooks, 

 and yet more definitely, Galton had reached the same 

 idea. From his experiments he was led in 1872 to the 



