Fig. H I. Section through the dorsal region of a _Pristiurus_-embryo in
which the rudimentary external gills are present as very small knobs.
Camera. (Zeiss CC, ocul. 2.)
The section shews the commencing differentiation of the posterior
nerve-rudiment into root (_pr_), ganglion (_sp.g_), and nerve (_n_), and
also the attachment of the nerve-root to the spinal cord (_x_). The
variations in the size and shape of the cells in the different parts of
the nerve-rudiment are completely lost in the figure.
_pr._ posterior nerve-root. _sp.g._ ganglion of posterior root. _n._
nerve of posterior root. _x._ attachment of posterior root to spinal
cord. _w._ white matter of spinal cord. _i._ mesoblastic investment to
the spinal cord.