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 majo- 

 rity perish under the disadvantages of external condi- 

 tions, because the oyster 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 

 generally shown itself derivable from similarity of de- 

 scent, we may now proceed to the explanation of those 

 phenomena of development known to us as hetero- 

 genesis and metamorphosis. In these, the historical 

 stages of development of whole classes and orders are 

 inherited in the development of the individual ; a pro- 

 position which is merely the corollary and application of 

 what has been already intimated. In no class is there 

 such a profusion of the phenomena of heterogenesis, 

 readily submitting to explanation, as in that of the 

 Medusae. We have already (p. 43) become acquainted 

 with the origin of the Cladonema from the polype-like 



