The nervous system of fishes is best studied in a specimen treated with nitric acid. Carefully remove the roof of the skull, thereby exposing the brain. Most anteriorly make out, as in the toad, the paired _olfactory lobes_. These are attached by long stalks to the _cerebrum_ or _forebrain_, which is followed by two large hollow lobes, the _midbrain_ or _optic lobes_. Behind the midbrain is the _cerebellum_. Following the cerebellum is the elongate _medulla oblongata_, which tapers backward into the _spinal cord_. How far backward does the spinal cord extend? On each side of the brain-case about opposite the cerebellum are located the _auditory organs_, each consisting of three _semicircular canals_ which lie in different planes, and of the _vestibule_. These parts are filled with liquid, and suspended in the liquid in the vestibule are small calcareous bodies called _otoliths_ or _ear-stones_. Running out beneath from the midbrain are the _optic nerves_, which cross, the left one connected with the right eye, the right one with the left eye. From each side of the medulla oblongata there is given off a large nerve, the _vagus_, which sends branches to the lateral line organs on either side, and extends backward to the stomach and viscera. For further study of the nervous system see Parker's "Zootomy," pp. 122-130. Make a drawing of the nervous system as worked out. TECHNICAL NOTE.--To make a good skeleton immerse a fresh or preserved specimen for some time in a hot soap solution. When the muscles have commenced to soften remove the body from the solution, pick the flesh away, and leave to dry. Note that the main axis of the _skeleton_ is composed of _vertebræ_ placed end to end. How many vertebræ are there? What vertebræ bear _ribs_? The ribless ones beyond the body-cavity are called _caudal vertebræ_. Note the _interspinal bones_ which support the fins, with large muscles on either side to control their action. Note that the group of bones supporting the pectoral fin is attached to the back of the brain-case and makes up the _shoulder girdle_. The ventral fins are attached to a rudimentary _pelvic girdle_, attached in front to the shoulder girdle, as the shoulder girdle is in turn attached to the skull. It will be seen that the sunfish has no neck and we may say, also, no back. Its skeleton consists only of a tail attached to the skull. The brain-case is made up of a number of bones closely joined together. From it is suspended the lower jaw, which comprises a number of bones but loosely attached to each other. Overlying these is the system of membrane bones already mentioned, including the opercle or gill-cover. For a detailed study of the fish-skeleton see Parker's "Zootomy," pp. 86-101, or Parker and Haswell's "Zoology," vol. II. pp. 183-195.