In an interesting paper published in 1844,[320] he discussed the relation
of this law of development to the problems of classification, and
arrived at results almost identical with those set forth by von Baer in
his Fifth Scholion.

Like von Baer he rejected completely the theory of parallelism and the
doctrine of the scale of beings; like von Baer he held that the type of
organisation--of which there are several--is manifested in the very
earliest stages and becomes increasingly specialised throughout the
course of further development; like von Baer, too, he sketched a
classification based upon embryological characters.

These views were further developed in his volume of 1851, and also in
his _Rapport_ of 1867.

They brought him into conflict with his confrere in the Academy of
Sciences, Etienne Serres, who in a number of papers published in the
'thirties and 'forties,[321] and particularly in his comprehensive memoir
of 1860, still maintained the theory of parallelism and the doctrine of
the absolute unity of type. His memoir of 1860 shows how completely
Serres was under the domination of transcendental ideas. Much of it
indeed goes back to Oken. "The animal kingdom," he writes, "may be
considered in its entirety as a single ideal and complex being" (p.
141). His views have become a little more complicated since his first
exposition of them in 1827, and he has been forced to modify in some
respects the rigour of his doctrine. But he still holds fast to the main
thesis of transcendentalism--the absolute unity of plan of all animals,
vertebrate and invertebrate alike,[322] the gradual perfecting of
organisation from monad to man, the repetition in the embryogeny of the
higher animals of the "zoogeny" of the lower.

He recognised, however, that the idea of a simple scale of beings is
only an abstraction, and that the true repetition is of organs rather
than of organisms. He was willing even to admit, at least in the later
pages of his memoir, that there might be not one animal series but
several parallel series, as had been suggested by Isidore Geoffroy St
Hilaire (p. 749). In general, his views are now less dogmatic than they
were in his earlier writings, but they are not for all that changed in
any essential. For, in summing up his main results, he writes, "The
whole animal kingdom can in some measure be regarded ideally as a single
animal, which, in the course of formation and metamorphosis in its
diverse manife