n epoch, may, it is
hoped, be considered as one step in the right direction towards a
complete solution of it.

_High Organization of very ancient Animals consistent with this Law._

Much discussion has of late years taken place on the question, whether
the succession of life upon the globe has been from a lower to a higher
degree of organization. The admitted facts seem to show that there has
been a general, but not a detailed progression. Mollusca and Radiata
existed before Vertebrata, and the progression from Fishes to Reptiles
and Mammalia, and also from the lower mammals to the higher, is
indisputable. On the other hand, it is said that the Mollusca and
Radiata of the very earliest periods were more highly organized than the
great mass of those now existing, and that the very first fishes that
have been discovered are by no means the lowest organised of the class.
Now it is believed the present hypothesis will harmonize with all these
facts, and in a great measure serve to explain them; for though it may
appear to some readers essentially a theory of progression, it is in
reality only one of gradual change. It is, however, by no means
difficult to show that a real progression in the scale of organization
is perfectly consistent with all the appearances, and even with apparent
retrogression, should such occur.

Returning to the analogy of a branching tree, as the best mode of
representing the natural arrangement of species and their successive
creation, let us suppose that at an early geological epoch any group
(say a class of the Mollusca) has attained to a great richness of
species and a high organization. Now let this great branch of allied
species, by geological mutations, be completely or partially destroyed.
Subsequently a new branch springs from the same trunk, that is to say,
new species are successively created, having for their antitypes the
same lower organized species which had served as the antitypes for the
former group, but which have survived the modified conditions which
destroyed it. This new group being subject to these altered conditions,
has modifications of structure and organization given to it, and
becomes the representative group of the former one in another geological
formation. It may, however, happen, that though later in time, the new
series of species may never attain to so high a degree of organization
as those preceding it, but in its turn become extinct, and give place to
yet an