rtebrae the parts of the skull
that lie beyond, such as the lateral processes of the cranium and the
facial plate, for they have no relation with the notochord" (p. 123).

To support this view he adduced the fact that the vertebral divisions
(primitive vertebrae) visible in the trunk do not extend into the head.
He used precisely the same arguments in his paper on _Alytes_ to destroy
the vertebral theory of the skull. We quote the following passage
translated by Huxley (1864, p. 295) from this paper. "It has therefore
become my distinct persuasion that the occipital vertebra is indeed a
true vertebra, but that everything which lies before it is not fashioned
upon the vertebrate type at all, and that efforts to interpret it in
such a way are vain; that, therefore, if we except that vertebra
(occipital) which ends the spinal column anteriorly, there are no
cranial vertebrae at all."

L. Agassiz, himself a pupil of Doellinger, in the general part (1844) of
his _Recherches sur les Poissons fossiles_ (Neuchatel, 1833-43), repeats
in the main his pupil Vogt's criticism of the vertebral theory (vol. i.,
pp. 125-9).

These arguments of Vogt and Agassiz were not considered by Mueller to
dispose of the theory,[217] which maintained a firm hold even upon
embryologists. It was still upheld by Reichert, and Koelliker in 1849
showed himself convinced of its general validity.

A useful step in the analysis of the concept "vertebra" was taken by
Remak,[218] who showed what a complex affair the formation of vertebrae
really is, involving as it does a complete resegmentation
(_Neugliederung_) of the vertebral column, whereby the original
vertebral bodies were replaced by the secondary definitive bodies (p.
143). Remak showed, as he thought, that the protovertebral segmentation
of the dorsal muscle-plates did not extend into the head, and he denied
Reichert's assertion (1837) that the cranial basis in mammals showed
transverse grooves delimiting three cranial vertebrae (p. 36). The
gill-slits, he considered, could not possibly be regarded as marking the
limits of head vertebrae.

In 1858 appeared Huxley's well-known Croonian Lecture, _On the Theory of
the Vertebrate Skull_,[219] in which he stated with great clearness and
force the case for the embryological method of determining homologies,
and criticised with vigour the vertebral theory of the skull. By this
time the two rival methods in morphology had become clearly
differentiate