22 NATURAL SCIENCE. yan., 
else could epiphyses ever be discriminated ? Again, the circumstance 
of a bone or cartilage making its appearance as a single element may 
in any case be due to the junction of its incipiently distinct parts ata 
period anterior to possible observation; it may be connate, i.e., never 
distinct to observation, though judged from analogy to be essentially 
multiple. Of such rationally-inferred but invisible distinctness, we 
have examples in botany. The vesults of development are surely as 
much to be considered as are its earlier stages. 
As to the vertebral or non-vertebral nature of the skull, it seems 
to us that such vertebral nature may be affirmed in one sense and 
denied in another, according to the line of thought which is followed. 
It is undeniable that it is within the /amine dorsales of the embryo 
that the cartilages and bones of both the brain-case and of the dorsal 
portion of the spinal cord are alike formed. Certainly also the bones 
of the skull—especially in the higher animals—present a singular 
reminiscence of vertebre in the three serially successive arches they 
form; and if the essence of vertebre consists in their being a series 
of bony rings fitted together, and serially enclosing the nervous 
centres, then, in that sense, the skull is in part composed of three 
vertebrze. In some fishes (e.g., the sturgeon) the transition from the 
spinal column to the skull is so gradual that the two are difficult to 
distinguish. In the Silurian fish Bagyus (as Owen pointed out) the 
vertebre next the head are greatly expanded, and join each other by 
suture, and this shows how undoubted vertebra may simulate osseous 
cranial walls. 
It is true that, unlike the nascent spinal column, the primitive 
skull presents no serial segmentation, and that the cartilaginous 
precursors of the cranial bones may even be divided medianly and 
antero-posteriorly. Nevertheless, in the young axolotl, before the 
base of the skull has become cartilaginous, an index of transverse 
segmentation is to be traced in the soft tissue of that region, in spite 
of the subsequent continuous chondrification of the base of the skull. 
But most striking of all is the return made? of late years by Sir 
Richard Owen’s main opponent to the conception that serial segmen- 
tation, however latent and disguised, extended primitively and funda- 
mentally to quite the anterior end of the head, and that, judging 
from Amphioxus, the skull of the higher vertebrates may be repre- 
sented as made up of something less than twenty serial segments, 
each of which is equivalent to a spinal vertebra with its annexed parts. 
The conception of cranial vertebrz, then, like the conceptions of 
serial, lateral, and general homology, are subjective apprehensions of 
relations having an objective existence in nature. They are like 
conception ‘types,’ which are not, of course, real objective 
entities, as types, though they are conceptions which have none the 
less an objective basis. The acceptance of the theory of evolution is 
no bar to the reception of the view which represents all organic forms 
Proc: Roy, SOC:, no! i57, p: £27: 
