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various stages of life, so far as the conditions of environment 
will allow.” 
If this were absolutely true—if the organism were like 
what its parent was at exactly the same age—it is difficult to 
understand how the dictum that ontogeny repeats phylogeny 
can be true. 
In order that ontogeny should repeat phylogeny it is 
evident that there must be a concentration of development. If 
the various phases of ontogeny represent the various develop- 
ments of the generations of species included in the genealogy 
of the individual, it is obvious that to find the various phases 
successively exhibited in the immature stages of the individual 
implies that they must have been inherited at an earlier and 
earlier time in the lives of individuals in successive generations. 
The more highly developed an organism is, the more stages 
must it pass through in order to reach maturity; and if 
these various stages each represent mature stages of less- 
developed forms it follows that the mature stages of earlier 
species become the immature stages of later species—in other 
words, that the adult stages of earlier species become adolescent 
stages of later species, and embryonic stages of still later 
species. 
What obtains in the successive species of a phylogenetic 
series must obtain, too, in the successive generations of a 
species. At the same time, it must be remembered that 
earlier inheritance would only be perceptible where there are 
developmental changes. In an organism which shews, practic- 
ally, no difference between, say, its adolescent and adult stages, 
except in the way of size, it is impossible to mark earlier 
inheritance; but for all that, it is reasonable to assume that 
the same law holds good as in the case of an organism in which 
there are marked differences to distinguish the various stages 
of life. Similarly it is an obvious fact that if the law of 
earlier inheritance be admitted to act in the phylogenetic 
series it must also be admitted to act in the generations of the 
species. 
