176 ESSAY ON CLASSIFICATION. 



they are satisfactorily known, may also be considered as 

 exemplifying, as it were, in the diversity of animals of an 

 earlier period, the pattern upon which the phases of the 

 development of other animals of a later period were to be 

 established. They now appear like a prophecy in those 

 earlier times of an order of things not possible with the 

 earlier combinations then prevailing in the animal king- 

 dom, but exhibiting in a later period, in a striking manner, 

 the antecedent consideration of every step in the grada- 

 tion of animals. 



This is, however, by no means the only, nor even the 

 most remarkable case, of such prophetic connections be- 

 tween facts of different dates. 



Eecent investigations in Palaeontology have led to the 

 discovery of relations between animals of past ages and 

 those now living, which were not even suspected by the 

 founders of that science. It has, for instance, been noticed 

 that certain types, which are frequently prominent among 

 the representatives of past ages, combine in their struc- 

 ture peculiarities which at later periods are only observed 

 separately in different, distinct types. Sauroid Fishes 

 existed before Eeptiles, Pterodactyles before Birds, Ich- 

 thyosauri before Dolphins, etc. 



There are entire families, among the representatives of 

 older periods, of nearly every class of animals, which, in 

 the state of their perfect development, exemplify such 

 prophetic relations, and afford, within the limits of the 

 animal kingdom at least, the most unexpected evidence 

 that the plan of the whole creation had been maturely 

 considered long before it was executed. Such types I 

 have for some time past been in the habit of calling pro- 

 phetic types. The Sauroid 1 Fishes of the past geological 



1 AGASSIZ (L.,) Poiss. foss., vol. 2, part 2. 



