The Animal Organism and its Germ-Layers 59 



Weismann is sufficiently explicit on this point. Not only 

 does IK- assume that germ-plasm cannot be produced by the 

 transformation of soinatoplasm, but he holds it cannot be 

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

 we read: "AIL 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." 5 



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, vi/.: the 'germ-plasm.' This sub- 

 stance can never be formed anew; it can only grow, multiply, 

 and be transmitted from one yenertttion 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 Krolution Theory, we find "I am forced to see in this 

 act 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 



nstitucnts, which can produce the complicated body solely 

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

 fluences, both extra- and intra-soiiiatic." 7 * 



The Exact Mode of Involvement of the Germ- pi asm Theory 

 in the Germ-Layer Theory 



We return now to the immediate point, namely that of 

 the- wav the germ-plasm doctrine involves the germ-layers. 



* While this is not the place 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 subject 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. 



in 



r: 



