RECAPITULATION AND CONCLUSION 435 



were produced? Were all the infinitely numerous 

 kinds of animals and plants created as egg's or seed, 

 or as full grown? and in the case of mammals, were 

 they created bearing the false marks of nourishment 

 from the mother's womb? Although naturalists very 

 properly demand a full explanation of every difficulty 

 from those who believe in the mutability of species, on 

 their own side they ignore the whole subject of the first 

 appearance of species in what they consider reverent 

 silence. 



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 may consider, by so much the arguments fall away 

 in force. But some arguments of the greatest weight 

 extend very far. All the members of whole classes can 

 be connected together by chains of affinities, and all 

 can be classified on the same principle, in groups sub- 

 ordinate to groups. Fossil remains sometimes 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 fully developed 

 state ; and this in some instances necessarily implies an 

 enormous amount of modification in the descendants. 

 Throughout whole classes various structures are formed 

 on the same pattern, and at an embryonic age the 

 species closely resemble each other. Therefore I can- 

 not doubt that the theory of descent with modification 

 embraces all the members of the same class. I believe 

 that animals have descended from at most only four 

 or five progenitors, and plants from an equal or lesser 

 number. 



Analogy would lead me one step further, namely, to 

 the belief that all animals and plants have descended 

 from some one prototype. But analogy may be a de- 

 ceitful guide. Nevertheless all living things have much 

 in common, in theirchemical composition, their germinal 

 vesicles, their cellular structure, and their laws of growth 

 and reproduction. We see this even in so trifling a 

 circumstance as that the same poison often similarly 



