ied for special functions, yet never so as to wholly mask their
typical character--then any given part of one segment may be repeated in
the rest of the series, just as one bone may be reproduced in the
skeletons of different species, and this kind of repetition or
representative relation in the segments of the same skeleton I call
'serial homology'" (p. 7). As an example of serial homology we might
take the centra of the vertebrae--the vomer, the presphenoid, the
basisphenoid, the basioccipital and the series of centra in the spinal
column. Such serially repeated parts are called _homotypes_ (p. 8).

Not all the bones of the vertebrate skeleton are included in the
archetype as constituents of the vertebrae. Thus the branchial and
pharyngeal arches are accounted part of the splanchnoskeleton, as
belonging to the same category as the heart bone of some ruminants, and
the ossicles of the stomach in the lobster (p. 70). The ossicles of the
ear in mammals are "peculiar mammalian productions in relation to the
exalted functions of a special organ of sense" (p. 140, f.n.). This
recognition of a possible development of new organs to meet new
functions shows unmistakably the influence of Cuvier. Owen was indeed
well aware of the importance of the functional aspect of living things,
and he often adopted the teleological point of view. As a true
morphologist, however, he held that the principle of adaptation does not
suffice to explain the existence of special homologies. The ossification
of the bones of the skull from separate centres may be purposive in
Eutheria, in that it prevents injury to the skull at birth; but how
explain on teleological principles the similar ossification from
separate centres in marsupials, birds and reptiles? How explain above
all the fact that the centres are the same in number and relative
position in all these groups? Surely we must accept the idea of an
archetype "on which it has pleased the divine Architect to build up
certain of his diversified living works" (p. 73).

In his study of centres of ossification, Owen made in point of theory a
distinct advance on his predecessors. We saw that Geoffroy recognised
the importance of studying the ossification of the skeleton, and that
Cuvier accepted such embryological evidence as an aid in determining
homologies. Owen pointed out that it was necessary to distinguish
between centres of ossification which were teleological in import and
such as were purel