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- 
*Delage: L’hérédité etc. P. 175—176. 
