55 
Reversion is of course only to be expected where the charac- 
ter reverted to belongs to a comparatively recent ancestor. 
Another mark of descent, reaching further back, is the 
presence of organs in a disused or rudimentary condition 
which formerly were of importance. When any organ becomes, 
from changes in the conditions of life, unused, the most pro- 
bable result would be that it should gradually become less 
and less perfectly developed ; at the same time it is quite 
conceivable that it should be retained for some time fully 
developed, though no longer of use. Both cases are found hi 
nature, the latter occasionally, as in the geese with webbed 
feet who never go into the water, and the woodpecker who 
never climbs a tree ; the former frequently, as in the rudimen- 
tary teeth of whales, the rudimentary tail in tailless animals, 
the rudimentary wings of the apteryx or ostrich, the rudimen- 
tary stamens in female flowers, &c. Both manifestly present 
great difficulties on the ordinary theory of special . creations, 
but fit in naturally with the Darwinian hypothesis of irre- 
gularly diverging common descent. 
Then to go a step farther back yet. Not only have we 
disused and rudimentary organs, but also organs differing 
enormously in development and use, yet radically identical, or 
even capable of transformation into one another. Thus the 
wing of a bird, the arm of a man, the paw of a lion, the 
flipper of a seal, are all strictly homologous structures, made 
up of similarly related and connected bones, though exter- 
nally so exceedingly different. Thus, again, in plants the 
different parts of the flower are seen occasionally to turn into 
mere leaves, showing the morphological identity of these so 
diverse organisms ; while in some cases, as the white water- 
lily, the transition from sepals to petals, and from petals to 
stamens, may be seen in all its fine gradations even in a single 
flower. All this is of course just what was to have been 
expected, if the Darwinian hypothesis of the common origin 
of species having homologous structures, and the enormous 
capability of variation possessed by every part, be accepted as 
true. On any other theory such phenomena are simply 
curious but inexplicable facts. 
Lastly, as the deepest-seated and farthest-reaching of all 
these marks of descent, we have the phenomena of embryo- 
logy. It was to be expected that if whole groups of living 
beings have really descended from a common progenitor by 
subsequent variation, the differences thus resulting should be 
developed in each individual somewhat later in time than 
those fundamental characters which all inherit in common ; in 
other words, that in the first stages of growth there should 
