THE STATE GEOLOGIST. 35 



est. Apart from its intrinsic interest, the study of fossil fishes 

 deserves a high place in our esteem on account of its having re- 

 vealed certain fundamental truths, the importance of which can- 

 scarcely be overestimated. One of the most far-reaching of these 

 in its later application is Louis Agassiz's discovery of the analogy 

 between embryological phases of recent fishes and the geological 

 succession of the class, which led him to a well defined conception 

 of what is commonly .called the "biogenetic law" : The history 

 of the. individual is but the epitomised history of the race. In thus 

 introducing the element of succession in time, Agassiz laid the 

 basis for all more recent embryological work. 



Another notable achievement arising from Agassiz's study of 

 fossil fishes was the recognition of so-called "embryonic," "pro- 

 phetic" or "synthetic" types, or such as combine in their structure 

 peculiarities which afterwards became distributed amongst dif- 

 ferent distinct types, and are never again recombined. Differ- 

 ences in the organization of fossil fishes led Agassiz to discrim- 

 inate between "lower" and "higher" forms, identical with the 

 generalized and more highly specialized types of modern zoolo- 

 gists. In the same way, Agassiz's "embryonic types," which he 

 held to "represent in their whole organization early stages of the 

 growth of higher representatives of the same type," are in many 

 cases the ancestral types of the modern evolutionist. 



A single illustration must suffice to show the application of 

 these important generalizations derived from the study of fossil 

 fishes. Agassiz, in the initial volume of his famous P'oissons 

 Fossiles, remarks more than once upon the fact that all fishes 

 antedating the Lias have the extremity of the vertebral column 

 deflected upward into a more or less prolonged caudal lobe, a 

 condition technically described as heterocercal. Subsequently he 

 observed that modern fishes exhibit a similar condition in their 

 early stages, though it was left for the younger Agassiz to demon- 

 strate that they faithfully reproduce ancestral characteristics,. 

 Adverting to this matter in his well-known "Essay on Classifica- 

 tion," Professor Agassiz remarks : "In my researches upon fossil 

 fishes, I have pointed out at length the embryonic character of 

 the oldest fishes, but much remains to be done in that direction. 

 The only fact of importance I have learned of late is that the 



