The Theory of Evolution 79 



of phylogeny. This view appears to stand in contradiction to 

 the biogenetic law. According to the formula that Haeckel 

 has maintained, the germ development is an epitome of the 

 genealogy ; or the ontogeny is a recapitulation of the 

 phylogeny ; or, more fully, the series of forms through which 

 the individual organism passes during its development from 

 the egg-cell to the finished condition is a short, compressed 

 repetition of the longer series of forms which the forefathers 

 of the same organism, or the stem-form of the species, has 

 passed through, from the earliest appearance of organisms to 

 the present time." " Haeckel admits that the parallel may 

 be obliterated, since much may be absent in the ontogeny 

 that formerly existed in the phylogeny. If the ontogeny were 

 complete, we could trace the whole ancestry." Hertwig states 

 further, that " The theory of biogenesis 1 makes it necessary 

 to change Haeckel's expression of the biogenetic law, so that 

 a contradiction contained in it may be removed. We must 

 drop the expression ' repetition of the form of extinct fore- 

 fathers,' and put in its place the repetition of forms which 

 are necessary for organic development, and lead from the 

 simple to the complex. This conception may be illustrated 

 by the egg-cell." 



Since each organism begins its life as an egg we must not 

 suppose that the primitive conditions of the time, when only 

 single-celled amcebas existed on our planet, are repeated. 

 The egg-cell of a living mammal is not, according to Hert- 

 wig's hypothesis, an indifferent structure without much spe- 

 cialization like an amoeba, but is an extraordinarily complex 

 end-product of a long historical process, which the organ- 

 ized substance has passed through. If the egg of a mam- 

 mal is different from that of a reptile, or of an amphibian, 



1 This term, by which Hertwig designates a particular view of his own, has 

 been already preoccupied in a much wider sense by Huxley to mean that all life 

 comes from preexisting life. Hertwig means by the theory of biogenesis that as 

 the egg develops there is a constant interchange between itself and its sur- 

 roundings. 



