6 HISTORICAL INTRODUCTION TO THE 



in the embryo while others are not ; that it is not because of their 

 being too small that they are not visible is clear, for the lung is of 

 greater size than the heart, and yet appears later than the heart 

 in the original development".^ 



Simple observation, therefore, had even in Aristotle's time given 

 the lie direct to the view that the embryo is a spatially preformed 

 miniature adult. Similar but more exhaustive and more crucial 

 observational evidence against the preformationist view was sup- 

 plied by William Harvey (who referred to development as '' epigene- 

 sin sive partium super additionem ") and, notably, by Caspar Fried- 

 rich Wolff. The conclusion to which the latter came is the same as 

 that of Aristotle. In the earliest stages of the development of the 

 fowl, the microscope reveals the presence of little globules heaped 

 together without coherence, and a miniature of the adult simply 

 does not exist. Further, no refuge can be taken in the assumption 

 that the miniature is too small to be seen, for its parts (globules) are 

 clearly visible, and, a fortiori, therefore, the whole. The plain fact 

 is that the miniature of the adult is not there. 



The necessary epigenetic correlate of this fact has been admirably 

 put by Delage in the following words :*' latent or potential characters 

 are absent characters. . . . The egg contains nothing beyond the 

 special physico-chemical constitution that confers upon it its in- 

 dividual properties qua cell. It is evident that this constitution is 

 the condition of future characters, but this condition is in the Qgg 

 extremely incomplete, and to say that it is complete but latent is to 

 falsify the state of affairs. What is lacking to complete the conditions 

 does not exist in the egg in a state of inhibition, but outside the egg 

 altogether, and can equally well occur or not occur at the required 

 moment. Ontogeny is fiot completely determined in the tgg ".^ We 

 might sum up the position by saying that to maintain the full pre- 

 formationist view would partake of the nature of fraudulent book- 

 keeping. 



There is no way of saving the view that the adult is preformed 

 in the egg as a diminutive replica. The more subtle idea of Bonnet's, 

 of preformed "organic points", or of determinants unequally dis- 

 tributed between the cells into which the tgg divides, also met its 

 doom a century ago, when Etienne Geoffroy St Hilaire (1826) experi- 



^ Quoted from Russell, loc. cit. 



