A U G U S T W E I S M A N N 337 



as far as their essential and characteristic substance is concerned, from 

 the body of the individual, but they are derived directly from the par- 

 ent germ-cell. 



I believe that the latter view is the true one: I have expounded it 

 for a number of years, and have attempted to defend it, and to work 

 out its further details in various publications. I propose to call it the 

 theory of "The Continuity of the Germ-plasm," for it is founded 

 upon the idea that heredity is brought about by the transference from 

 one generation to another of a substance with a definite chemical, and 

 above all, molecular constitution. I have called this substance "germ- 

 plasm," and have assumed that it possesses a highly complex structure, 

 conferring upon it the power of developing into a complex organism. 

 I have attempted to explain heredity by supposing that in each on- 

 togeny a part of the specific germ-plasm contained in the parent egg- 

 cell is not used up in the construction of the body of the offspring, 

 but is reserved unchanged for the formation of the germ-cells of the 

 following generation. 



It is clear that this view of the origin of germ-cells explains the 

 phenomena of heredity very simply, inasmuch as heredity becomes 

 thus a question of growth and of assimilation, — the most fundamental 

 of all vital phenomena. If the germ-cells of successive generations 

 are directly continuous, and thus only form, as it were, different parts 

 of the same substance, it follows that these cells must, or at any rate 

 may, possess the same molecular constitution, and that they would 

 therefore pass through exactly the same stages under certain condi- 

 tions of development, and would form the same final product. The 

 hypothesis of the continuity of the germ-plasm gives an identical start- 

 ing point to each successive generation, and thus explains how it is 

 that an identical product arises from all of them. In other words, the 

 hypothesis explains heredity as part of the underlying problems of as- 

 similation and of the causes which act directly during ontogeny ; it 

 therefore builds a foundation from which the explanation of these 

 phenomena can be attempted. 



It is true that this theory also meets with difficulties, for it seems to 

 be unable to do justice to a certain class of phenomena, viz., the trans- 

 mission of so-called acquired characters. I therefore gave immediate 

 and special attention to this point in my first publication on heredity, 

 and I believe that I have shown that the hypothesis of the transmis- 



