V. 



Hertwig's " Preformation or New Formation." ' 



Part I. 



DR. OSCAR HERTWIG has worked so long at embryological 

 subjects, and has produced results so valuable, that his opinion 

 on this burning question of to-day is of unusual value. It is 

 proposed in this paper to give an uncritical account of the views 

 expressed by him in his most recent publication. 



Biologists of the seventeenth and eighteenth centuries observed 

 the process of embryological development as the growth of a 

 miniature but visible embryo or bud into the adult form. They 

 regarded it, therefore, as a process in which the minute particles 

 of a formed organism became bigger by the absorption and trans- 

 formation of food-substances. By analogical reasoning they carried 

 these visible occurrences back to invisible beginnings, and came to 

 hold the germ of an organism as a miniature image of the adult, 

 invisible to us on account of the imperfection of our eyes, and 

 by reason of the extreme minuteness and opacity of the germ. They 

 had got beyond "the idea of spontaneous generation, and had for- 

 mulated a theory of the continuity of life in the phrases " omne 

 vivum e vivo," and " omne vivum ex ovo." And so, in addition 

 to the theory of " preformation," they adopted the theory of " evolu- 

 tion." The germ of an animal was a miniature of the animal, 

 and within this, germ within germ, were enfolded the germs of all 

 future descendants of the animal. The succession of the generations 

 of animals was an "evolution," or unrolling of a series of germs 

 arranged by the Creator at the beginning of the world. 



In the last hundred years improvement of methods and instru- 

 ments has carried the boundaries of the visible much further into 

 matter. The embryos and buds which appeared then simple organic 

 substance are now resolved into milHons of cells, while these again are 



1 Zeit- und Streitfragen der Biologie. By Professor Dr. Oscar Hertwig. 

 Pamphlet I. Praeformation oder Epigenese ? Grundziige einer Entwicklungs- 

 theorie der Organismen. Pp. 144, with 4 illustrations in the text. Gustav 

 Fischer, 1S94. Price 3 marks. 



