EARLIEST TYPES OF ANIMALS. 33 



three other great types of the animal kingdom, since fishes 

 exist wherever Eadiata, Mollusks and Articulata are 

 found together, and the plan of structure of these four 

 great types constitutes a system intimately connected in 

 its very essence. Moreover, for the last twenty years 

 every extensive investigation among the oldest fossilifer- 

 ous rocks has carried the origin of Vertebrata step by step 

 further back ; so that, whatever may be the final solution 

 of this vexed question, so much is already established by 

 innumerable facts, that the idea of a gradual succession 

 of Eacliata, Mollusks, Articulata and Vertebrata is for ever 

 out of the question. It is proved beyond doubt, that Ea- 

 diata, Mollusca and Articulata are everywhere found toge- 

 ther in the oldest geological formations, and that very early 

 Vertebrata are associated with them and have continued 

 to be so through all geological ages to the present time. 

 This shows that even in those early days of the existence 

 of our globe, when its surface did not yet present those 

 diversified features which it has exhibited in later periods, 

 and which it exhibits in still greater variety now, animals 

 belonging to all the great types now represented upon 

 earth were simultaneously called into existence. It shows 

 further, that, unless the physical elements then at work 

 themselves devised such plans, and impressed them 

 upon the material world as the pattern upon which 

 Nature was to build for ever afterwards, no such general 

 relations as exist among all animals of all geological 

 periods as well as among those now living, could ever 

 have existed. 



This is not all : every class among Eadiata, Mollusks 

 and Articulata is known to have been represented in those 

 earliest days, with the exception of the Acalephs 1 and 



1 Acalephs have been found in the Their absence in other formations 

 Jurassic Limestone of Solenhofen. may be owing simply to the extraor- 



D 



