iv ZIEGLER ON INHERITANCE 185 



mission of acquired characters was conceivable ; and Darwin, 

 by his " pangenesis," and Haeckel, by his theory that repro- 

 duction and heredity depend on the transference of a definite 

 form of motion (motion of the plastidula) from the parental 

 organs to the organic molecules of the generative cells, offered 

 an explanation of the phenomenon of the inheritance of ac- 

 quired characters considered by both as proved. But Ziegler 

 says that since newer researches have shown that fertilisation 

 is a purely morphological process, the inheritance of acquired 

 characters is excluded. This view is further supported by 

 the argument that the sexual cells are not elements which 

 could be derived from any cells of the organism whatever. 

 The nuclei of an organ of the fully-developed organism could 

 only possess by inheritance the property of producing, with 

 the aid of the cell-protoplasm, tissue of a single kind. The 

 structure of the sexual cells, on the other hand, must be 

 so constituted, that from the offspring of two nuclei which 

 coalesce, all the cells of the individual body, including new 

 sexual cells, can arise. 



I have already expressed my opinion upon the view which 

 regards reproduction as a purely morphological process. I 

 should hold it no less justifiable to regard life in general as a 

 morphological process, for reproduction is a part of the life of 

 the organic world. 



That the sexual cells give rise to not only one, but to the 

 several kinds of tissue-cells, is their most peculiar (specific) 

 function in multicellular animals ; but if multicellular animals 

 have been derived from unicellular, this distinction cannot be 

 a fundamental one, and must have been evolved in course of 

 time as an acquired and inherited property. Since the 

 cause of the evolution of this distinction can only depend on 

 the advantage of division of labour, following upon the ad- 

 vantage previously gained by colonial life, and division of 

 labour consists in physiological relations between the cells of 



