459] _Vergleich. Anat. d. Wirbelthiere_, i., pp. 200-1,
1898.

[460] For a full historical account of work on membrane
and cartilage bones (as well as on the theory of the
skull) see E. Gaupp, "Altere und neuere Arbeiten ueber
den Wirbelthierschaedel," _Ergeb. Anat. Entw._, x., 1901,
and "Die Entwickelung des Kopfskelettes," in Hertwig's
"_Handbuch vergl. exper. Entwickelungslehre d.
Wirbelthiere_," iii., 2, pp. 573-874, 1905.

[461] "Les Ancetres des Marsupiaux etaient-ils
arboricoles?" _Trav. Stat. zool. Wimereux_, vii., pp.
188-203, pls. xi.-xii., 1899. See also Bensley, _Trans.
Linn. Soc._ (2) ix., pp. 83-214, 1903.

[462] _Proc. Zool. Soc._, pp. 649-62, 1880. _Sci. Mem._,
iv., pp. 457-72.

[463] J. F. Gemmill, _Phil. Trans. B_, ccv., p. 255, 1914.

CHAPTER XVIII

THE BEGINNINGS OF CAUSAL MORPHOLOGY

Until well into the 'eighties animal morphology remained a purely
descriptive science, content to state and summarise the relations
between the coexistent and successive form-states of the same and of
different animals. No serious attempt had been made to discover the
causes which led to the production of form in the individual and in the
race.

It is true that evolution-theory had offered a simple solution of the
great problem of the unity in diversity of animal forms, but this
solution was formal merely, and went little beyond that abstract
deduction of more complex from simpler forms, which had been the main
operation of pre-evolutionary morphology. Little was known of the actual
causes of ontogeny, and nothing at all of the causes of phylogeny; it
was, for instance, mere rhetoric on Haeckel's part to proclaim that
phylogeny was the mechanical cause of ontogeny.

Animal physiology, on its side, had developed in complete isolation from
morphology into a science of the functioning of the adult and finished
animal, considered as a more or less stable physico-chemical mechanism.
Since the days of Ludwig, Claude Bernard and E. du Bois Reymond, the
physiologists' chief care had been to analyse vital activities into
their component physical and chemical processes, and to trace out the
interchange of matter and energy between the organism and its
environment. Physiologists had left untouched, perhaps wisely, the much
more difficult problem of the causes of the development of form. For all
practical purposes they took the animal-machine as given,