312 THE HISTORY OF CREATION. 



animals — in the different classes, families, and species of it 

 — have unequally developed, differentiated, and perfected 

 themselves. It shows us how far the succession of classes 

 of vertebrate animals, from the Fishes upwards, through the 

 Amphibia to the Mammals, and here again, from the 

 lower to the higher orders of Mammals, forms a progressive 

 series or ladder. This attempt to establish a connected 

 anatomical developmental series we may discover in the 

 works of the great comparative anatomists of all ages — 

 in the works of Goethe, Meckel, Cuvier, Johannes Miiller, 

 Gegenbaur, and Huxley. 



The developmental series of mature forms, which com- 

 parative anatomy points out in the different diverging and 

 ascending steps of the organic system, and which we call 

 the systematic developmental series, is parallel to the 

 palseontological developmental series, because it deals with 

 the result of pal^eontolgical development, and it is parallel 

 to the individual developmental series, because this is 

 parallel to the palseontological series. If two parallels are 

 parallel to a third, they must be parallel to one another. 



The varied differentiation, and the unequal degree of per- 

 fecting which comparative anatomy points out in the 

 developmental series of the System, is chiefly determined 

 by the ever increasing variety of conditions of existence to 

 which the different groups adapt themselves in the struggle 

 for life, and by the different degrees of rapidity and com- 

 pleteness with which this adaptation has been effected. 

 Conservative groups wdiich have retained their inherited 

 peculiarities most tenaciously remain, in consequence, at the 

 lowest and rudest stage of development. Those groups pro- 

 gressing most rapidly and variously, and which have adapted 



