red
with each other.

But is there a transition from Radiates to Mollusks, or from Articulates
to Vertebrates, or from any one of these divisions into any other? Let
us first consider the classes as they stand within their divisions. We
have seen that there are three classes of Radiates,--Polyps, Acalephs,
and Echinoderms; three classes of Mollusks,--Acephala, Gasteropoda, and
Cephalopoda; three classes of Articulates,--Worms, Crustacea, and
Insects; and, according to the usually accepted classification, four
classes of Vertebrates,--Fishes, Reptiles, Birds, and Mammalia. If there
is indeed a transition between all these classes, it must become clear
to us, when we have accurately interpreted their relative standing.
Taking first the lowest branch, how do the classes stand within the
limits of the type of Radiates? I think I have said enough of these
different classes to show that Polyps as a whole are inferior to
Acalephs as a whole, and that Acalephs as a whole are inferior to
Echinoderms as a whole. But if they are linked together as a connected
series, then the lowest Acaleph should stand next in structure above the
highest Polyp, and the lowest Echinoderm next above the highest Acaleph.
So far from this being the case, there are, on the contrary, many
Acalephs which, in their specialization, are unquestionably lower in the
scale of life than some Polyps, while there are some Echinoderms lower
in the same sense than many Acalephs. This remark applies equally to the
classes within the other types; they stand, as an average, relatively to
each other, lower and higher, but considered in their diversified
specification, there are some members of the higher classes that are
inferior in organization to some members of the lower classes. The same
is true of the great divisions as compared with each other. Instead of
the highest Radiates being always lower in organization than the lowest
Mollusks, there are many Star-Fishes and Sea-Urchins higher in
organization than some Mollusks; and so when we pass from this branch to
the Articulates, if we assume for the moment, as some naturalists
believe, that the Mollusks are the inferior type, the Cuttle-Fishes are
certainly very superior animals to most of the Worms; and passing from
Articulates to Vertebrates, not only are there Insects of a more complex
organization than the lowest Fishes, but we bring together two kinds of
animals so remote from each other in structure that the