nal sinus, and then cut down
through body wall into this just over gill slits. The tenth nerve will
become visible, with its "slit" branches athwart the floor of the sinus.
Clear to make this more evident, and make out its lateral line and
visceral branches, and the ninth nerve.

{Lines from Second Edition only.}
[The pharyngo-branchials may be felt beneath the sinus. Run a
seeker from the dorsal aorta to the efferent branchials.]

Proceed now to orbit, and, without any dissection beyond the removal
of skin, make out recti and oblique muscles of eyeball, and the optic,
third and fourth nerves. Cut through these structures carefully and
remove, exposing nerves seven, and five, as described and figured in
the text. Examine the otic capsule by taking successive slices
through it to show the labyrinth of the ear. -Remove the dorsal wall of
the skull to obtain a dorsal view of brain. If this is sufficiently hard,
examine it; if not, return it to spirit for a more convenient occasion.-
[Examine brain.]

-Amphioxus_

Two specimens of this type should be obtained. It should be
examined entire by the naked eye and with the low power of the
microscope. Immersion, in glycerine will render it more transparent; or
it may be cleared with oil of cloves, put up temporarily in that, or
permanently in Canada balsam. One specimen should then be pinned
out in the dissecting dish, ventral side uppermost, and the atrium
opened to expose liver and pharynx. A part of the pharynx may be
examined with the low power to see the form of the gill slits. The
second specimen should be soaked in turpentine for some time, and
then dropped into melted paraffin wax. Transverse sections may then
be cut with a razor, the paraffin wax removed from these by solution in
turpentine, the turpentine in its turn dissolved out by alcohol, and the
sections, after immersion in oil of cloves, may be transferred to
Canada balsam for examination and preservation. This work should
not be attempted until some practical histological work has been done
in botany, and it may be altogether avoided by the purchase of
stained and mounted sections.

-Development_

Laboratory work in this portion of the science is not usually
undertaken by elementary students of biology, but the reader will
probably find it helpful, in the realization of the facts given in this
book, to look out for frog spawn, in February and March, and to catch
and examine tadpoles of vari