242 Theories Treating of Inheritance 



as appears from his own words here quoted, that if the 

 organism appears to pass again during ontogeny through 

 the preceding phyletic stages this depends merely upon 

 the fact that there is no other materially possible way for 

 the idioplasm to attain the phylogenetic equilibrium just 

 acquired. 



But to accept this is to deny the law of repetition. 



One notes that Hertwig was lead to reject this law, as 

 he himself admits, only because he wished to avoid the 

 objection which Weismann had already urged against 

 Nageli ; namely that if one supposes that different phylo- 

 genetic forms may be due to respective idioplasms qual- 

 itatively different from one another it is not possible to 

 understand how the same forms when they succeed one 

 another in the ontogeny of a single species can then 

 depend only upon "different conditions of tension and 

 movement," of one and the same idioplasm. 



But it seems to us that Hertwig has attempted in vain 

 to circumvent this obstacle. 



"A very general and very astonishing fact," writes 

 Delage, "is that ontogeny almost never follows a direct 

 and simple course. The cells almost never dispose them- 

 selves from the beginning in the order which would bring 

 the embryo soonest to its final conformation. Ontogeny 

 approaches its goal gradually, but as though compelled to 

 tack against a contrary wind, and its long tacks carry it 

 sometimes far to the side. It shapes a number of rudi- 

 ments, permits purposeless members to arise, opens gill 

 clefts in a lung breathing animal only to close them again, 

 and so on." 186 



These tacks, these deviations hither and thither, cer- 



180 Delage: L'heredite etc. P. 175176. 



