scopeofzoology

ideas in comparative anatomy that began in the late l9th century came to an abrupt end at
the outbreak of the second World War. In 1945 a new generation of zoologists was in
command of research, and it was the comparative experimental approach to physiology that
surged forward. The achievements of the D'Arcy Thompson/Huxley school were left behind
as a blind end to a particular research philosophy. It is only now, with a marriage between
biochemistry and developmental biology that we are beginning to understand the operation of
growth mechanisms during development, and to some extent to explain the precise
mathematical analyses of the organism in relation to its parts that were carried out between
1900 and 1939.
Current approaches to the study of size and shape can be traced to the beginnings of
experimental developmental biology. Historically, the study of development as a process
began, not with the final product of ontogeny, which was the mainstay of dynastic zoology,
but with the developing embryo. In the 1930's experimental embryology had much the same
appeal as molecular biology has today, in that students felt it to be the most promising
advancing front of biological research. This was partly because histological analysis in early
development showed that unity existed between animal dynasties previously separated in
terms of gross anatomy. Further, differentiation proceeded uniformly through the mobilisation
and deployment of similarly structured cellular envelopes, tubes and sheets in all animals.
Chemical unity of evolution was also apparent in the topical organiser theory, which
postulated that differentiation in development is the outcome of an orderly sequence of
limited but specific chemical stimuli. The underlying assumption of the theory was that an
understanding of the chemical properties of the inductive agent would reveal why the amino
acid sequence of proteins should differ. Unfortunately the rapid rise of experimental
embryology tended to segregate various aspects of the life-cycle as distinct topics within the
zoology syllabus, such as differentiation, growth, maturation and ageing, which is only now
being overcome. For example, it is currently felt that life should be viewed more as a
continuum at the chemical level; ageing and embryonic growth have a unity.
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