80 THE DOCTRINE OF DESCENT. 
to the present day. The formations mostly have their 
characteristic organisms, but almost everywhere the con- 
necting links have been exhibited. Everything conduces 
to show that it is a question of evolution, not revolution. 
Wherever there seems to be a sudden break, the case is 
the same as in the revolutions of human history, in which 
likewise only reforms long-prepared, and practically 
necessary, come to a rapid issue. 
If we sum up the result of the comparison of fossil with 
living animal life, we are first of all struck by the accord- 
ance between the grades succeeding one another in the 
order of time, and the members now ranged side by side 
in the system. Secondly, when this is confirmed, the 
parallelism between the geological succession of animals 
and the grades of the individual development of present 
animals follows as a matter of course. Agassiz, in his 
great work on fossil fishes, pointed out this fact with 
irresistible force, and confirmed it in his later writings by 
renewed, valuable, and convincing observations on the 
investigations of the development and growth of corals. 
The same examples which served in the preceding 
chapter to illustrate the parallelism of individual de- 
velopment with the systematic stages, may be repeated 
here; though many newer and very striking instances 
have been brought to light by the special researches 
of the last ten years. To express this relation, Agassiz 
introduced the term “embryonic types,” or “embryonic 
representatives.” Thus the stalked stone-lilies are the 
embryonic types of the present genus Comatula; the 
most ancient Echinz are the embryonic representatives 
of the higher families of the Clypeastrze and Spatange; 
the Mastodon, on account of its persistent molar teeth, 
