DOCTRINE OF ORGANIC EVOLUTION (435 
having wings and feathers like a bird, but with the toothed 
jaws and long, jointed tail of a reptile were discovered in 
rocks of just the age required by the theory. 
Such backward reasoning of course yields trustworthy 
results largely in proportion to the fulness of our knowledge 
regarding all the forms of the group studied, and all stages of 
their life. The younger stages are especially noteworthy in 
tracing kinship, for it has been found as a general rule that 
the earlier the stage at which related organisms are com- 
pared the closer are the resemblances. We have already seen 
an example of this rule in our comparison of the development 
of flowers belonging to the crowfoot and the bluebell types. 
If we compare such flowers as those in Figs. 298, and 299 I 
we find that in the earliest stage both have five distinct petals; 
but while in the rose these petals continue to grow separate, 
in the oxeye the whole corolla-base soon begins to grow as a 
continuous ring carrying upward the petal rudiments so that 
they finally appear as teeth or projections on the margin of a 
bell. Hence, we may suppose a degree of kinship between 
the rose and the oxeye, or the flax (Fig. 217 II) and the blue- 
bell (Fig. 299 II), which a comparison of their mature flowers 
would not so clearly reveal, and the fact that the mature 
corolla of the rose is essentially like the young corolla of the 
oxeye indicates that the ancestor common to both was more 
like a rose than an oxeye; or in other words, that the bluebell 
type of corolla has been the more highly evolved, while that 
of flax or rose has more nearly retained the ancestral form. 
Many such facts incline evolutionists to believe that the 
successive stages passed through by an individual in its 
development correspond more or less closely to the various 
forms which appeared successively in its line of ancestry. 
The development of an individual organism from egg to adult 
is termed its ontogeny,: while the evolution of the group to which it 
belongs is distinguished by the term phylogeny.? It is commonly 
accepted as a general rule by evolutionists that ontogeny epitomizes 
phylogeny, and this is called the law of recapitulation. We shall have 
occasion, however, to notice in our attempts to apply this law in the 
1 On-tog’en-y < Gr. onta, things existing; gennao, to produce. 
2 Phy-log’en-y < Gr. phylon, a tribe. 
