402 PROGRESS OF SCIENCE IN THE CENTURY. 



The first attempt at an objective answer is ex- 

 pressed in a theory which seems to have occurred at 

 intervals throughout the centuries, the theory of pan- 

 genesis. It was hinted at by Democritus, Hippoc- 

 rates, Paracelsus, Maupertuis, and Buffon. It was 

 suggested as a provisional hypothesis by Darwin and 

 also by Spencer (1864). According to the theory of 

 pangenesis, the cells of the body are supposed to give 

 off characteristic and representative gemmules, these 

 are supposed to find their way to the reproductive 

 elements, which thus come to contain, as it were, 

 concentrated samples of the different components of 

 the body, and are therefore able to develop into an 

 offspring like the parent. The theory involves many 

 hypotheses, and is avowedly unverifiable in direct 

 sense-experience, but the same might be said about 

 many other theories. It is perhaps more to the 

 point to notice that there is another theory of heredity 

 which is, on the whole, simpler, which seems, on 

 the whole, to fit the facts better, especially the fact 

 that our experience does not warrant the conclusion 

 that the modifications or acquired characters of the 

 body of the parent affect in any specific and repre- 

 sentative way the inheritance of the offspring. 



As we have already hinted, the view which many, 

 if not most biologists now take of the uniqueness of 

 the germ-cells is rather different from that of pan- 

 genesis. It is expressed in the phrase "germinal 

 continuity," and was suggested by several thinkers 

 Ovren, Hacckel, Jaeger, Brooks, Galton, and Nuss- 

 baum before Weismann worked it out into a con- 

 sistent theory. In many cases, scattered through 

 the animal kingdom, from worms to fishes, the be- 

 ginning of the lineage of germ-cells is demonstrable 

 in very early stages before the differentiation of tho 



