[461] "Les Ancêtres des Marsupiaux étaient-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, and did not trouble about its mode of origin. They held indeed that form-production was due to a complex of physico-chemical causes, which they hoped some day to unravel;[464] but this future physiology of development remained quite embryonic.