See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1861
1869
1872

certain mammals or of the whole class 1861 1866
the whole class of mammals, or of certain members in this class, 1869 1872

of, and thus exterminating, 1861 1866 1869
of 1872

compared with fishes. 1861 1866
in comparison with fishes. 1869
in having to come continually to the surface to breathe. 1872

1 blocks not present in 1859 1860 1861 1866; present in 1869 1872
In this latter class, members of the shark family would not tend to supplant the lancelet; for the lancelet, as I hear from Fritz Müller, has as sole companion and competitor on the barren sandy shore of South Brazil, an anomalous annelid.

they have existed in 1861 1866
their 1869 1872

which, as already explained, 1861 1866
have 1869 1872

and in nearly every class, 1861 1866
OMIT 1869 1872

favourable variations 1861 1866
variations or individual differences of a favourable nature 1869
variations or individual differences of a favorable nature 1872

invertebrate classes. But mammals and fish hardly come into competition with each other; the advancement of certain mammals or of the whole class to the highest grade
of organisation
of organisation
would not lead to their taking the place of, and thus exterminating, fishes. Physiologists believe that the brain must be bathed by warm blood to be highly active, and this requires
aërial
aërial
respiration; so that warm-blooded mammals when inhabiting the water
lie
live
under
a
some
disadvantage
disadvantages
compared with fishes. In this latter class, members of the shark family would not, it is probable, tend to supplant the
amphioxus;
lancelet;
the struggle for existence in the case of the
amphioxus
lancelet
apparently will lie with members of the invertebrate classes. The three lowest orders of mammals, namely, marsupials, edentata, and rodents, co-exist in South America in the same region with numerous monkeys, and probably interfere little with each other. Although organisation, on the whole, may have advanced and be
still advancing
advancing
throughout the world, yet the scale will
always
still
present
many
all
degrees of perfection; for the high advancement of certain whole classes, or of certain members of each class, does not at all necessarily lead to the extinction of those groups with which they do not enter into close competition. In some cases, as we shall hereafter see, lowly organised forms
appear
seem
to have been preserved to the present
day,
day
from inhabiting
confined
peculiar
or
peculiar
isolated
stations, where they have been subjected to less severe competition, and where they have existed in scanty
numbers
numbers,
which, as already explained,
retarded
retards
the chance of
favorable
favourable
variations arising.
Finally, I believe that
many lowly
lowly
organised forms now exist
in numbers
in numbers
throughout the world, and in nearly every class, from various causes. In some cases favourable variations may never have arisen for natural
selection
selec- tion