292 THE HISTORY OF CREATION. 



simply and meclianically by the action of natural selection 

 in the struggle for life. 



The infinitely important study of rudimentary organs and 

 their origin, the comparison of their palseontological and 

 embryological development, now naturally leads us to the 

 consideration of one of the most important and instructive 

 of all biological phenomena, namely, the parallelism which 

 the phenomena of progress and divergence present to us in 

 three difierent series. When, in the last chapter, we spoke 

 of perfecting and division of labour, we understood by 

 those words progress and separation, and those changes 

 effected by them, which in the long and slow course of the 

 earth's history have led to a continual variation of the 

 flora and fauna, to the origin of new and to the disappear- 

 ance of ancient species of animals and plants. Now, 

 if we follow the origin, the development, and the life 

 of every single organic individual, we meet with exactly 

 the same phenomena of progress and differentiation. The 

 individual development, or the ontogenesis of every single 

 organism, from the egg to the complete form is nothing 

 but a growth attended by a series of diverging and pro- 

 gressive changes. This applies equally to animals, plants, 

 and protista. If, for example, we consider the ontogeny 

 of any mammal, of man, of an ape, or of a pouched 

 animal, or if we follow the individual development of any 

 other vertebrate animal of another class, we everywhere 

 find essentially the same phenomena. Every one of 

 these animals develops itself originally out of a single cell, 

 the egg. This cell increases by self-division, and forms a 

 number of cells, and by the growth of this accumulation of 

 cells, by the divergent development of originally identical 



