202 THE DOCTRINE OF DESCENT. 



If the concatenation of the series by direct derivation 

 and heredity be disallowed, it is absolutely inconceiv- 

 able 'why the supreme creative Power, Nature, or the 

 personal God, should have bound all higher animals to 

 the same common stages of early development, and here- 

 by exposed them to such manifold purposeless arrange- 

 ments and great dangers. Of the millions of young 

 oysters which annually escape from the egg, the ma- 

 jority perish under the disadvantages of external condi- 

 tions, because the ayster has not yet divested itself of 

 the ancient heirloom of the roving navicula. It has been 

 able to compete successfully in the struggle for existence, 

 only because, like most of its congeners, it is enormously 

 prolific. This may be understood; but that a personal 

 Creator, merely on principle, in order to keep the oyster 

 within the type of development, should have, endowed it 

 with the phase of the navicula, in this case so extremely 

 unpractical, can be accepted, like much other nonsense, 

 only as matter of faith. 



If accordance in the outlines of development has gen- 

 erally shown itself derivable from similarity of descent, 

 we may now proceed to the explanation of those phe- 

 nomena of development known to us as heterogenesis 

 and metamorphosis. In these, the historical stages of 

 development of whole classes and orders are inherited 

 in the development of the individual ; a proposition which 

 is merely the corollary and application of what has been 

 already intimated. The Hydromeduras offer numbers of 

 such instances of heterogenesis, of which Gegenbaur's 

 early views gives the following account : We have already 

 (p. 43) become acquainted with the origin of the 

 Cladonema from the polype-like Stauridium. The 



