484 
CONCLUSION. 
Chap. XIV. 
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 their chemical composition, their germinal 
vesicles, their cellular structure, and their laws of growth 
and reproduction. We see this even in so trifling a cir¬ 
cumstance as that the same poison often similarly affects 
plants and animals; or that the poison secreted by the 
gall-fly produces monstrous growths on the wild rose or 
oak-tree. Therefore I should infer from analogy that 
probably all the organic beings which have ever lived 
on this earth have descended from some one primordial 
form, into which life was first breathed by the Creator. 
When the views advanced by me in this volume, 
and by Mr. Wallace in the Linnean Journal, or when 
analogous views on the origin of species are generally 
