EVOLUTION AND EPIGENESIS. 20J 



velopment which drove Bonnet and Haller to the other ex- 

 treme ? Who reproached the "evolutionists" for having 

 adopted an hypothesis that excluded explanation with miracle ? 

 Who are to-day elaborating mechanical theories of develop- 

 ment ? Who undertake to refer the polarity of the egg to 

 such mechanics as "geocentric differentiation," or to some 

 wholly accidental circumstance in fecundation ? Who claimed 

 to have found the long-sought vis directrix in gravity, and by 

 the force of his brilliant example, started an avalanche of 

 theories from which no delivery is yet in sight ? Is the doc- 

 trine of "directive stimuli " less theoretical than that of deter- 

 minants ? Is the epigenesis of so-called " dynamic evolution " 

 conspicuously free from theory ? 



The claim to a monopoly of fact is obviously a pure epige- 

 netic origination deserving notice only because it reflects an 

 arrogance which seems to be epidemic, though generally held 

 in more insidious reserve. 



Oscar Hertwig proceeds with more cautious circumspection, 

 and with a clearer perception of the fundamental differences 

 between the old and the new theories of development; but he 

 labors with ingenuity to show that epigenesis opens the door 

 to investigation while evolution offers the dangerous " Ruhe- 

 kissen " to our desires for a causal explanation of development. 

 Hertwig concludes his able essay on " Praformation oder Epi- 

 genese.-* " with the following grave indictment: 



" The doctrine of determinants has thrown back the mystery, 

 which we might hope at least partially to resolve by investi- 

 gation of the properties of visible forms, into an invisible 

 region where there is absolutely no point of attack for research. 

 Thus by its very nature it remains unfruitful for research, to 

 which it can offer no possible way of advance. In this respect 

 it resembles its predecessor, the preformation theory of the 

 1 8th century." 1 



Had not the doctrine of determinants already proved a most 

 powerful stimulus to research, and had not Hertwig himself 

 conceded the principle of determinants, at least for such char- 

 acters as can be realized in the cell for itself (p. 84), his indict- 



1 Zeit- und Streitfrageii der Biologic, 1894, p. 137. Cf. pp. 11, 12. 



