680 Studies in the Theory of Descent. 



from their first origination, bear in themselves a 

 tendency to show individual peculiarities, and 

 would develop these even if they should not be 

 again affected by dissimilar influences. This is 

 obviously the case, since the youngest egg-cells in 

 the ovary of an animal are, as can be demon- 

 strated, always exposed to unequal external con- 

 ditions with respect to nutrition and pressure. 16 

 Hence, if it were possible that two germs were 

 exactly equal with respect to the direction of 

 development imparted to them by heredity, they 

 would nevertheless furnish two incongruent indi- 

 viduals ; and if, conversely, it were possible that 

 two individuals could be exposed to absolutely 

 the same external influences from the formation 

 of the embryo, these also could not be identical, 

 because the individual differences of the ancestors 

 would entail small differences, even in asexual 

 reproduction, in the direction of development 

 transmitted to the egg. The differences between 

 individuals of similar origin thus finally depend 

 entirely upon the dissimilarity of external in- 

 fluences on the one side upon those which divert 

 the development of the progenitors, and on the 

 other side upon those which divert the individual 

 itself from its course, i. e. from the developmental 

 direction transmitted hereditarily. Although I 

 thus essentially agree with Darwin and Haeckel 



10 See Haeckel's "Generelle Morphologic," vol. ii. p. 203, 

 and Seidlitz, " Die Uarwin'sche Theorie," 1875, p. 92 ft. seq. 



