The Animal Organism and its Germ-Layers 59 



Weismann is sufficiently explicit on this point. Not only 

 does he assume that gcrni-plasm cannot be j)roduced by the 

 transformation of somatoplasm, but he holds it cannot be 

 produced in any other way. Touching' the more special case 

 we read: "All these facts support the assumption that so- 

 matic idioplasm is never transformed into germ-plasm, and 

 this conclusion forms the basis of the theory of the compo- 

 sition of the germ-plasm as propounded here." ^ 



A fairly typical expression of the author's all-embracing 

 denial of new germ-plasm is the following: "The off- 

 spring owes its origin to a peculiar substance of extremely 

 complicated structure, viz.: the 'germ-])hism.' This sub- 

 stance can never he formed anew; it can onlij grow, multiply, 

 and he transmitted from one generation to another. '"^ '^ A 

 form of expression much used by Weismann particularly in 

 his later writings, which somewhat disguises though does 

 not surrender the main point, is that of "primary con- 

 stituents" of the germinal substance. Thus in his discus- 

 sion of the germ-plasm doctrine in his last extensive work, 

 The Evolution Theory, we find "I am forced to see in this 

 fact alone [that of metamorphosis in ontogeny] an invalida- 

 tion of all epigenetic theories of development, that is of all 

 theories which assume a germ-substance without primary 

 constituents, which can produce the complicated body solely 

 by varying step by step under the influence of external in- 

 fluences, both extra- and intra-somatic."''' * 



The Exact Mode of Involvement of the Germ-plasm Theory 



in the Germ-Layer Theory 



We return now to the immediate point, namely that of 



the way the germ-plasm doctrine involves the genn-layers. 



* While this is not the phice to point out in detail the far-reaching 

 consequences of this assumed impossibility of new formation in or- 

 ganic evolution, much less to show the subtle fallacy which it involves, 

 the general sul)ject is so important and will loom up so greatly in our 

 enterprise as a whole, that I would wish to get it well into the read- 

 er's attention even at this early stage of our progress. 



