THE ORIGIN OF THE FORMS OF LIFE. 45 
in a more ancient form, but serve no use in the creatures in 
which they are now found, have reached, it is thought, their 
rudimentary condition through long periods of comparative 
disuse, in many generations. Such are the, rudimentary mus- 
cles of the ears of man, or the undeveloped incisor teeth found 
in the upper jaw of ruminants. 
5. Geographical Distribution.—It can not be said that animals 
and plants are always found in the localities where they are 
best fitted to flourish. This has been well illustrated within 
the lifetime of the present generation, for the animals intro- 
duced into Australia have many of them so multiplied as to 
displace the forms native to that country. But, if we assume 
that migrations of animals and transmutations of species have 
taken place, this difficulty is in great part removed. 
6. Paleontology.—The rocks bear record to the former exist- 
ence of a succession of related forms; and, though all the in- 
termediate links that probably existed have not been found, 
the apparent discrepancy can be explained by the nature of 
the circumstances under which fossil forms are preserved; and 
the “imperfection of the geological record.” 
Itis only in the sedimentary rocks arising from mud that 
fossils can be preserved, and those animals alone with hard 
parts are likely to leave a trace behind them; while if these 
sedimentary rocks with their inclosed fossils should, owing to 
enormous pressure or heat be greatly changed (metamorphosed), 
all trace of fossils must disappear—so that the earliest forms 
of life, those that would most naturally, if preserved at all, be 
found in the most ancient rocks, are wanting, in consequence 
of the metamorphism which such formations have undergone. 
Moreover, our knowledge of the animal remains in the earth’s 
crust is as yet very incomplete, though, the more it is explored, 
the more the evidence gathers force in favor of organic evolu- 
tion. But it must be remembered that those groups constitut- 
ing species are in geological time intermediate links. 
%, Fossil and Existing Species.—If the animals and plants now 
peopling the earth were entirely different from those that flour- 
ished in the past, the objections to the doctrine of descent would 
be greatly strengthened; but when it is found that there is in 
some cases a scarcely broken succession of forms, great force is 
added to the arguments by which we are led to infer the con- 
nection of all forms with one another. 
To illustrate by a single instance: the existing group of 
horses, with a single toe to each foot, was preceded in geological 
