ature of Limbs_, p. 49)--the embryo shows a greater
resemblance to the archetype than the adult. "We perceive a return to
it, as it were, in the early phases of development of the highest
organised of the actually existing species, or we ought rather to say
that development starts from the old point; and thus, in regard to the
scapula, we can explain the constancy of its first appearance close to
the head, whether in the human embryo or in that of the swan, also its
vertical position to the axis of the spinal column, by its general
homology as the rib or 'pleurapophysis' of the occipital
vertebra" (_Limbs_, p. 56).

We owe to Owen the first clear distinction between "homologous" and
"analogous" organs; it was he who first proposed the terms "homologue"
and "analogue," which he defined as follows:--"_Analogue_. A part or
organ in one animal which has the same function as another part or organ
in a different animal." "_Homologue_. The same organ in different
animals under every variety of form and function."[165]

He introduced also useful distinctions between Special, General, and
Serial Homology. "The relations of homology," he writes, "are of three
kinds: the first is that above defined, viz., the correspondency of a
part or organ, determined by its relative position and connections, with
a part or organ in a different animal; the determination of which
homology indicates that such animals are constructed on a common type;
when, for example, the correspondence of the basilar process of the
human occipital bone with the distinct bone called 'basi-occipital' in a
fish or crocodile is shown, the _special homology_ of that process is
determined. A higher relation of homology is that in which a part or
series of parts stands to the fundamental or general type, and its
enunciation involves and implies a knowledge of the type on which a
natural group of animals, the Vertebrate, for example, is constructed.
Thus when the basilar process of the human occipital bone is determined
to be the 'centrum' or 'body' of the last cranial vertebra, its _general
homology_ is enunciated.

"If it be admitted that the general type of the vertebrate endoskeleton
is rightly represented by the idea of a series of essentially similar
segments succeeding each other longitudinally from one end of the body
to the other, such segments being for the most part composed of pieces
similar in number and arrangement, and though sometimes extremely
modif