TECHNICAL NOTE.--In a specimen which has been macerated for some time in 20% nitric acid dissect out the nervous system. Place the specimen in a pan ventral side uppermost and pin out. Carefully pick away the vertebræ and the roof of the mouth-cavity, thereby exposing the central nervous system, which will appear light yellow. Examine the _brain_. In front of the true brain are the _olfactory lobes_, the nervous centre for the sense of smell. The brain itself is composed of several parts. The anterior portion consists of two elongated parts, the _cerebral hemispheres_; just back of these are the optic lobes or _midbrain_, consisting of two short lobes, which are followed by the small _cerebellum_, which in turn is followed by a long part, the _medulla oblongata_, which runs imperceptibly into the long dorsal nerve, the _spinal cord_. Note the large _optic nerves_ running out to each eye. How far backward does the spinal cord extend? Note the many pairs of nerves given off from the brain and spinal cord. These nerves branch and subdivide until they end in very fine fibres. Some end in the muscle-fibres, and through them the central nervous system innervates the muscles. These are _motor endings_. Still others pass to the surface and receive impressions from the outside. These last are _sensory endings_. Note that the _spinal nerves_ arise from the spinal cord by two roots, an _anterior_ or _ventral_, and a _posterior_ or _dorsal root_. Trace the principal spinal nerves to the body-parts innervated by them. These nerves are numbered as first, second, etc., according to the number of the vertebræ (counting from the head backward) from behind which they arise. CHAPTER III THE STRUCTURE AND FUNCTIONS OF THE ANIMAL BODY =Organs and functions.=--The body of the toad is composed of various parts, such as the lungs, the heart, the muscles, the eyes, the stomach, and others. The life of the toad consists of the performance by it of various processes, such as breathing, digesting food, circulating blood, moving, seeing, and others. These various processes are performed by the various parts of the body. The parts of the body are called _organs_, and the processes (or work) they perform are called their _functions_. The lungs are the principal organs for the function of breathing; the heart, arteries and veins are the organs which have for their function the circulation of the blood; the principal organ concerned in the digestion of food is the alimentary canal, the function of seeing is performed by the organs of sight, the eyes, and so one might continue the catalogue of all the organs of the body and of all the functions performed by the animal.