28 ESSAY ON CLASSIFICATION 



the ultimate details of structure which in different genera bear 

 definite relations to those of other genera; the mode of differentia- 

 tion of species, and the nature of their relations to the surrounding 

 media must likewise have been determined, as the character of the 

 classes is as well defined as that of the four great branches of the 

 animal kingdom, or that of the families, the genera, and the species. 

 Again, the first representatives of each class stand in definite relations 

 to their successors in later periods, and as their order of apparition 

 corresponds to the various degrees of complication in their structure 

 and forms a natural series closely linked together, this natural grada- 

 tion must have been contemplated from the very beginning.^^ There 

 can be the less doubt upon this point, as man, who comes last, closes 

 in his own cycle a series, the gradation of which points from the very 

 beginning to him as its last term. I think it can be shown by anatom- 

 ical evidence that man is not only the last and highest among the 

 living beings, for the present period, but that he is the last term of a 

 series beyond which there is no material progress possible upon the 

 plan upon which the whole animal kingdom is constructed, and that 

 the only improvement we may look to upon earth for the future 

 must consist in the development of man's intellectual and moral 

 faculties.^^ 



The question has been raised of late how far the oldest fossils 

 known may truly be the remains of the first inhabitants of our globe. 

 No doubt extensive tracts of fossiliferous rocks have been intensely 

 altered by plutonic agencies, and their organic contents so entirely 

 destroyed, and the rocks themselves so deeply metamorphosed, that 

 they resemble now more closely eruptive rocks even than stratified 

 deposits. Such changes have taken place again and again up to com- 

 paratively recent periods and upon a very large scale. Yet there are 

 entire continents. North America, for instance, in which the palaeo- 

 zoic rocks have undergone little if any alteration, and where the re- 

 mains of the earliest representatives of the animal and vegetable king- 

 doms are as well preserved as in later formations. In such deposits 

 the evidence is satisfactory that a variety of animals belonging to 

 different classes of the great branches of the animal kingdom have 

 existed simultaneously from the beginning; so that the assumption of 



^ [To an evolutionist of course this fact is primary evidence of genetic affiliation.] 

 "Agassiz, An Introduction to the Study of Natural History (New York, 1847), p. 57. 



