352 THE EVOLUTION THEORY 



This cortninly m arked considera ble progress, for it meant the 

 l»e«'-innint>- of a science of embryology, that is. the science o f the 

 form-development of the animal or plant from the ovu m. The 

 result was not so important in its theoretical aspect, for though the 

 knt)\vloilge had been gained that the young animal goes through 

 a lone series of ditferent stao-es, it had not been discovered how 

 nature works this wonder and causes an animal of complex 

 structure to arise from the apparently simple substance of the ovum. 

 A solution of the difficulty was found by attributing to the ovum 

 a formative power, afterwards called by Blumenbach the nisufi 

 format ii'ii!<, which possessed the capacity of developing a complex 

 animal from the simple 'slime,' or, as we should say, the simple 

 protoplasm. 



If we contrast the strictly theoretical part of the two theories, 

 we find that Bonnet regar ded the ovum as something only apparently 

 simple, but in reality almost as complex as the animal_ ^which 

 d evelop ed from it, a nd that he thought of the latter, not as being 

 formetlanew, but as being unfolded or evolved. That is to say, he 

 thoughttliat rudiments prese ntTrom the outset in the ov jim^gxadually 

 r evealed t he mselves and became visible. Wo lff, on the other han d, 

 regarded the ovu m as beiqg what ^t seemed, someth ing quite simple, 

 out of which only the inzmtjoriimtivus could , by_ a__serias. of 

 transformatiDTi 5"'and new formatl O&s, build up a new organism of the 

 re levant specie s. 



Wolff's Epigenesis routed Bonnet's theory so completely from the 

 field that, until quite recently, epigenesis was regarded as the onlj- 

 scientifically justifiable theory, and a return to the ' evolutionist ' 

 position would have been looked upon as a retrograde step, as 

 a reversion to a period of fancy which had been happily passed. 

 I mj'self have been repeatedly told, with regard to my own 

 ' evolutionistic ' theory, that the correctness of epigenesis was in- 

 disputably established, that is, was a fact, verifiable at any time 

 by actual observation ! 



But what are the facts ? Surely only that there is a succession 

 of numerous developmental stages, which we know very precisely 

 in the case of a great many animals, and that the miniature model 

 wdiich Bonnet assumed to be in the egg does not exist. Both these 

 facts are now no longer called in question. But that does not furnish 

 us with a theory of development, for theory is not the observation 

 of phenomena or of a series of phenomena, it is the interpretation 

 of thera. Epigenesis, as formulated first by Aristotle and again by 

 Harvey, Wolff, and Blumenbach, o(^rhf^\^^\J off(^rpr|_aiT_jTTj;,f^r|ii:<:>ift^,inn 



