8o THE DOCTRINE OF DESCENT. 



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 ne- 

 cessary, 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 

 accordance 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 ani- 

 mals 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 by fresh, valuable, and 

 convincing observations in his later works, down to his 

 investigations as to the development and growth of 

 corals. The same examples which served in the preced- 

 ing 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 in- 

 troduced the term " embryonic types," or " embryonic 

 representatives." Thus the stalked stone lilies are the 

 embryonic types of the present genus Comatula; -the 

 most ancient Echinidae are the embryonic representatives 

 of the higher families of the Clypeastrae and Spatangidse; 

 the Mastodon, on account of its persistent molar teeth, 

 is the embryonic type of the elephant, which only transi- 

 torily possesses such teeth. If the term implies nothing 

 further than the vague assertion of " the working of the 

 same creative Mind through all times and upon the whole 



