ture of living things merit some
attention. Organic forms, according to Owen, result from the
antagonistic working of two principles, of which one brings about a
vegetative repetition of structure, while the other, a teleological
principle, shapes the living thing to its functions. The former
principle is illustrated in the archetype of the vertebrate skeleton, in
the segmentation of the Articulates, in the almost mathematical symmetry
of Echinoderms, and the actually crystalline spicules of sponges. It is
the same principle which causes repetition of the forms of crystals in
the inorganic world. "The repetition of similar segments in a vertebral
column, and of similar elements in a vertebral segment, is analogous to
the repetition of similar crystals as the result of polarising force in
the growth of an inorganic body" (p. 171). This "general polarising
force" it is which mainly produces the similarity of forms, the
repetition of parts, and generally the signs of the unity of
organisation. The adaptive or "special organising force" or [Greek:
idea], on the other hand, produces the diversity of organic beings. In
every species these two forces are at work, and the extent to which the
general polarising or "vegetative-repetition-force" is subdued by the
teleological is an index of the grade of the species.

This view is analogous to the Geoffroyan conception that the diversity
of form is limited by the unity of plan. Owen thus ranges himself with
Geoffroy against Cuvier, who considered that diversity of form is
limited only by the principle of the adaptation of parts.

[164] Owen introduced most of the names of bones now
current.

[165] _Lectures on Invertebrate Animals_, pp. 374, 379,
1843.

CHAPTER IX

KARL ERNST VON BAER

Von Baer was recognised as the founder of embryology even by his
contemporaries. His predecessors, Aristotle,[166] Fabricius,[167]
Harvey,[168] Malpighi,[169] Haller,[170] Wolff,[171] had made a
beginning with the study of development; von Baer, by the thoroughness
of his observation and the strength of his analysis, made embryology a
science.

It was to one of the German transcendentalists that von Baer owed the
impulse to study development. Ignatius Doellinger, Professor in Wuerzburg,
induced three of his pupils, Pander, d'Alton and von Baer, to devote
themselves to embryological research. The development of animals was at
this time little known, in spite of recent