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! 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 amcoebas 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 amceba, 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 preéxisting life. | Hertwig means by the theory of biogenesis that as 
the egg develops there is « constant interchange between itself and its sur- 
roundings. 
