And yet, according to the teaching of the school, it is precisely in
youth, precisely in the course of development, that the "Type" is mostly
openly displayed. But let us hear what the Old School has to tell us as
to the significance of developmental history, and its relation to
comparative anatomy and systematic zoology.
Let two of its most approved masters speak.
"Whilst comparative anatomy," said Johannes Muller, in 1844, in his
lectures upon this science (and the opinions of my memorable teacher
were for many years my own), "whilst comparative anatomy shows us the
infinitely multifarious formation of the same organ in the Animal
Kingdom, it furnishes us at the same time with the means, by the
comparison of these various forms, of recognising the truly essential,
the type of these organs, and separating therefrom everything
unessential. In this, developmental history serves it as a check or
test. Thus, as the idea of development is not that of mere increase of
size, but that of progress from what is not yet distinguished, but which
potentially contains the distinction in itself, to the actually
distinct,--it is clear, that the less an organ is developed, so much the
more does it approach the type, and that, during its development, it
more and more acquires peculiarities. The types discovered by
comparative anatomy and developmental history must therefore agree.
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