DEVELOPMENT. 277 



organization. Reptiles first appear in the Carboniferous strata, 

 and arrive at their full development in the Triassic and Jurassic 

 formations. The Mammalia announce themselves, as it were, 

 by a few prophetic species in the Upper Trias and the Jura ; but 

 these species belong to the Marsupials, which present the lowest 

 grade of organization in the class, and the Mammalia only attain 

 their great importance in Tertiary times (see vol. i. p. 275) . 

 The Palaeozoic period may therefore be characterized as that of 

 Cryptogams and Fishes, the Secondary as that of Gymnosperms 

 and Reptiles, and the Tertiary as that of Dicotyledons and Mam- 

 mals. Lastly, as the crowning achievement of the whole crea- 

 tion, appears Man, who, by his intellectual faculties, raises him- 

 self above all other animals, and is enabled not only to understand 

 the laws of nature, and in some degree to subjugate Nature to 

 his will, but also to find his God in the works of nature, and to 

 become himself conscious of his own eternal destiny. 



In the appearance of plants and animals in different geological 

 ages a progressive development according to natural laws is 

 manifested, beginning with the lower and more simply con- 

 structed forms and continued on to more highly organized crea- 

 tures ; and since this course of development has found its term 

 in Man, no new species has been produced. 



It must not, however, be imagined that in this gradual. ad- 

 vance of organic nature link has followed link in a consecutive 

 series ; for instead of the highest plants approaching the lowest 

 animals, it is found that the simplest unicellular animals are so 

 nearly allied to the simplest plants that between them a line of 

 demarkation can hardly be drawn. Consequently there is a 

 common starting-point for the two kingdoms of nature as re- 

 gards their simplest organisms ; but on quitting this point each 

 kingdom takes a special direction in its development, and their 

 respective advances might very well be compared to a tree, which, 

 branching in all directions, puts forth innumerable leaves and 

 flowers, representing the existing fauna and flora. 



The fundamdntal cause of this progressive development of the 

 organic world in accordance with a definite plan must be innate ; 

 for the material elements were always the same, whilst the living 

 creatures into which they enter are in a state of continual change, 

 and present an infinite variety of forms and modes of organiza- 



