August. 1894- " PREFORMATION OR NEW FORMATION." 133 



ordered aggregates of physical substances. Although in this minuter 

 investigation no trace has been found of enfolding of germ within 

 germ, yet as a logical possibility this theory could only fail when the 

 actual limits Of matter had been reached. It remains to-day as it 

 was at origin, unfounded on observed fact, but in the limits of pure 

 reason logically tenable. 



Wolff's "Theoria Generationis " was the foundation of epigenetic 

 views. He perceived that preformation and evolution formed a closed 

 system where there was no room for the progress of research. He 

 tried to bring back embryology from pure reason to the realms of 

 observation, and held that the germs of animals and plants were 

 structureless organic matter, which in the process of development by 

 new formation or epigenesis became the organised adult. His theory 

 found little favour in his own day, for he could offer no rounded in- 

 terpretation of nature in which the mind of man could dwell. He 

 had no explanation of that " vis essentialis," inherent energy, with 

 which he endowed organic matter ; on his system the growth of a new 

 organism remained as much a miracle as he declared the theory of 

 germ within germ to imply. 



Since his time, succeeding generations have done something to 

 place a real meaning within his inspiring but empty phrase, and in the 

 slow progress of science step after step has been taken in tracing 

 the forces and methods by which organic forms arise. But to-day, 

 as formerly, the same question is answered in two ways. In the 

 words of Roux : — "Is embryological development epigenesis or 

 evolution ? Is it a new formation of structure? or is it the becoming 

 visible of structure previously invisible to us ? " 



Weismann is the great modern instance of those who respond for 

 preformation and evolution. According to him, each cell or set of 

 cells of the adult that vary independently have an actual representative 

 in the germ. The germ is a microcosm in the strict sense of the 

 word, and this microcosm is a miniature of the adult invisible to our 

 eyes. In two respects, Weismann's germinal microcosm differs from 

 that of the older evolutionists. They held it to be a simple and direct 

 miniature of the adult. For us, separated from those times by a 

 century of embryological work, the actual events of embryological 

 development, the visible changes of cell-layers, and the metamorphoses 

 of organs, make this view untenable. And so in Weismann's micro- 

 cosm the elements representing structures in the adult are arranged 

 quite differently from the adult arrangement. Secondly, the older 

 evolutionists explained the chain of life by their theory of germ within 

 germ. Weismann attributes to his microcosm the power of division. 

 But in method and tendency this modern theory of preformation, 

 like the older theory, stays rather than satisfies the desire for causal 

 explanations, and is on the intellectual level of an " explanation " of 

 the origin of the world by supernatural means. 



For many years Dr. Oscar Hertwig has been studying both the 



