ory organs of fish greatly resemble
those of tadpoles the conclusion has been drawn that fish are in a sense
embryos of Amphibia (p. 547). But this manner of viewing things is none
the less vicious, "for this reason ... that it considers only one or two
points and neglects all the others" (p. 548), and is directly contrary
to common sense. There is never a recapitulation of total organisations,
only at the most of single organs.

It will be remembered that Cuvier opposed and demolished the theory of
the _Echelle des etres_, not only by showing that there were in Nature
four entirely different plans of animal structure, but also by
demonstrating that even the animals of each single _Embranchement_ could
not readily be arranged in one series, that a serial arrangement was
really valid only for their separate organs. Von Baer also held that
there are four distinct types of structure; he, too, combated the idea
of gradation within the limits of the type. In so far as species
represent successive stages in the development, the _Ausbildung_, of the
type, so far can the idea of a scale of beings be applied. But the
members of a type follow not one line of evolution but several diverging
lines, in direct adaptation to different environmental conditions, so
that a serial arrangement of them is not as a rule possible. It may be
possible to establish a serial arrangement of single organs from the
simplest to the most complex. But each organ or organ-system will
require a different serial arrangement, for the different systems vary
on different lines and an animal may be highly developed in respect of
one system and little developed in respect of all the others. Man, for
instance, is the highest animal only in respect of his nervous system.
The idea of the scale of beings has therefore only a very limited
application even within the limits of the type. Applied to the whole
animal kingdom it becomes merely absurd.

Another point of resemblance between Cuvier and von Baer was that
Cuvier, though essentially a student of adult structure, did recognise
the importance of embryology; following up some observations of
Dutrochet he studied the foetal membrane of mammals and tried to
establish their homologies.[180] And in his criticism of the vertebral
theory of the skull he advanced as an argument against the
basisphenoid being a vertebral centrum the fact (established
by Kerkring, 1670), that it develops from two centres.[181] Von Baer'