298 CONCLUSION. [Chap. XV. 



There are, however, some who still think that species 

 have suddenly given birth, through quite unexplained 

 means, to new and totally different forms : but, as I 

 have attempted to show, weighty evidence can be op- 

 posed to the admission of great and abrupt modifications. 

 Under a scientific point of view, and as leading to further 

 investigation, but little advantage is gained by believing 

 that new forms are suddenly developed in an inexplic- 

 able manner from old and widely different forms, over 

 the old belief in the creation of species from the dust of 

 the earth. 



It may be asked how far I extend the doctrine of the 

 modification of species. The question is difficult to 

 answer, because the more distinct the forms are which 

 we consider, by so much the arguments in favour of 

 community of descent become fewer in number and 

 less in force. But some arguments of the greatest 

 weight extend very far. All the members of whole 

 classes are connected together by a chain of affinities, 

 and all can be classed on the same principle, in 

 groups subordinate to groups. Fossil remains some- 

 times tend to fill up very wide intervals between 

 existing orders. 



Organs in a rudimentary condition plainly show that 

 an early progenitor had the organ in a fuUy developed 

 condition ; and this in some cases implies an enormous 

 amount of modification in the descendants. Throughout 

 whole classes various structures are formed on the same 

 pattern, and at a very early age the embryos closely 

 resemble each other. Therefore I cannot doubt that the 

 theory of descent with modification embraces all the 

 members of the same great class or kingdom. I believe 

 that animals are descended from at most only four or 



